P0505 and P0506 in 2026: Idle Valve, Throttle Body, Air Leak or Software — What 341 Documents and 2,200 Complaints Show

P0505 and P0506 are codes about a number, not a part. The engine computer picks an idle speed for the conditions it sees and moves the throttle, or on older engines a separate idle air control valve, to hold it. P0506 — printed by GM as "Idle Speed Low" and by Stellantis as "Idle Speed Performance Lower Than Expected" — says the engine ran slower than the computer asked for, long enough to set a code. P0505, the idle control system code, says the system failed a check of its own. Neither says why.

This page answers one question: why does my idle hunt, surge, drop too low or stall, and is it the idle air control valve, the throttle body, a leak or the computer; can I drive; what does it cost. The high idle, P0507, has its own page. The cold-start cousins P050A (Kia prints it as "Cold Start Idle Air Control System Performance") and P050B (Stellantis prints it as "Cold Start Ignition Timing Performance") appear in a few papers (JTB00532NAS1, a Kia Soul bulletin).

The headline. The papers that print these codes almost never blame an idle air control valve. Across the 341 documents the printed causes are a charge air cooler pipe that comes off the throttle body (GM 1.5L turbo), a broken valve spring (GM V8 trucks), loose intake manifold bolts, a vacuum plug that fell out of an intake manifold (Land Rover), split crankcase-ventilation membranes, car-wash water vapor, engine software, a torque converter whose one-way clutch is misaligned (2026 Hyundai) and, in two papers (GM PIP4578B and a Toyota tech tip), throttle body deposits; a third, GM PIT3116B, prints only a cleaning. No document tells a shop to replace an idle air control valve for a low or unstable idle. Of the 1,015 complaints that describe the fault, 714 (70%) state no cause or leave it unknown, and 80 more (8%) say a shop checked and found nothing.

What the page rests on. NHTSA's index lists 1,292 carmaker papers whose summary names a code of this family or uses idle wording; from those, and 57 more found by an independent check, we went through 341 distinct documents, chosen as the method note states, and the filings of four recalls (three discussed here, all four in Sources). We also went through 2,200 federal owner complaints received from January 2015 through early October 2026, of which 1,015 describe a low, hunting or stalling idle or an idle-control repair and 1,185 do not. Only 23 of the 1,015 print P0505 or P0506; the rest describe a low or unstable idle without naming either code, so read every count as "complaints describing this fault", not "P0506 complaints". Counts are complaints, not cars; nothing is a failure rate.

Is a low or hunting idle usually the idle air control valve, and should that be the first part you buy? PulsCar went through 341 distinct carmaker documents and 2,200 federal owner complaints, 1,015 of which describe an idle problem. No document tells a shop to replace an idle air control valve for that fault. The causes the papers print are a boost pipe off the throttle body, a broken valve spring, loose intake manifold bolts, a split crankcase-ventilation diaphragm, software and, on two 2026 Hyundais, a torque converter. In the complaints, 11 end at an idle valve (5% of the 221 that name any cause), 31 at a throttle body (14%) and 93 at fuel, ignition or engine mechanics (42%), while 714 name no cause and 80 more say a shop found nothing. Read the code, ask for the software level and the air path first, and test before buying a part.

🟢 marks a claim resting on a document in the Sources section; ⚪ marks a shop-price estimate from our repair guides. Every complaint count comes from the 2,200 sorted twice and published; owner-reported figures are what people told NHTSA, published with NHTSA complaint numbers, and the documents are listed.

Words on this page. Papers: carmakers' bulletins and recall filings; their numbers (PIP, SSM, NTB and so on) are the makers' own; quote the number to the dealer. DTC: fault code. MIL: the check engine light. ECM, PCM, ECU, DME: the engine computer; TCM: the transmission computer. Freeze frame: the speed, temperature and load the computer saves when a code sets; a scan tool can read it. Flash: software update. IAC valve: the separate idle air control valve on older engines. Relearn: letting the computer relearn the idle throttle opening. PCV: crankcase ventilation. CVT: a gearless automatic. Smoke test: a shop blows harmless smoke into the intake to find leaks. Fuel trims: how much the computer is correcting the fuel for air it did not meter.

I built PulsCar after a $380 "full diagnostic" in Phuket in 2025 led to roughly $6,000 over six months across several shops (the story is on the About page).

What P0505 and P0506 say: the engine ran slower than the computer asked

The target and the result. On a modern car there is no idle screw. The computer sets a target speed from engine temperature, the air conditioner, the electrical load and the gear, and opens the throttle just enough to hold it. P0506 records a gap on the low side that lasted too long. 🟢 Hyundai prints "P050500 Idle Air Control System" and "P050600 Idle Air Control System - RPM Lower than Expected", Lexus prints "P0505 - Idle Control System", and the 6.7L Cummins flashes print "P0506-00 - Idle Control System RPM - Lower Than Expected."

Why the computer can lose. Air it cannot meter (a pipe off, a hose, a plug), a throttle with deposits or no relearn, a wrong airflow reading, software that judges the wrong thing, or an engine that cannot make the power: a broken valve spring, a leaking purge valve, a torque converter that does not let go at a stop.

What the codes are not. They do not say the idle valve or the throttle body is bad. 🟢 On the 2026 Palisade Hybrid, Hyundai's own event text for P0505 and P0506 reads "P0505/P0506 MISDIAGNOSIS" beside "ECU S/W TO IMPROVE DTC": the fix is engine software, not a part. And in most of the documents, P0506 is one code in a long list: in the Stellantis flashes the list can run from about 10 to about 40 codes.

Who prints P0505 at all. Ten of the 341 documents print P0505, from six repair stories. Eighty print P0506, mostly inside lists.

First: is your idle actually wrong?

The computer changes the idle on purpose when the air conditioner cuts in, the engine is cold or the battery is low. The documents print few numbers for what is left in and more for what the maker treats as a fault; the first row below is a variation GM leaves in, the other three are faults fixed with software.

The test that separates normal from a fault. A designed change has a reason you can name (the compressor engaged, the engine is cold, a load came on) and settles. A fault does not settle, drops the engine toward stalling, repeats at stops, or comes with a code or a light. 🟢 GM's police Tahoe sheet: "A/C cycling may cause approx. 100 rpm idle speed variation for example from 650 to 550 rpm"; Toyota prints the Scion FR-S fault as "idle speed fluctuates (typically 500 – 1000 RPM)". Two makers say the opposite of alarm: 🟢 Mercedes (version 3 of its bulletin), "The idle fluctuation typically resolves after several trips and will not cause other drivability symptoms or damage to the vehicle."; Ford, "Inform customers that they can continue to drive the vehicle".

The maker atlas: who prints P0506 or a low-idle stall, and what they blame

Bulletin numbers are linked to NHTSA's PDF.

The pattern. 🟢 Where a paper names a hardware cause for P0506, it is something that changes the air or the power, almost never the idle valve. Where it names software (for a low or unstable idle, with or without a code), it names the engine computer, the hybrid controller, the transmission computer or, in one GM paper that sets no code (18-NA-328), the climate-control (HVAC) module.

The do-not-replace lines: what the papers tell a shop to hold back

• GM 1.5L turbo with P0506 in the list (PIP5651C and D, 22-NA-224): 🟢 "The throttle body and mass airflow (MAF) sensor associated with the listed codes should only be replaced if they are damaged or found to be the cause of the code."
• GM intake manifold bolts (PIP5529A and B): 🟢 "Do not replace the intake manifold gasket unless testing indicates the gasket is leaking after the bolts are torqued."
• Land Rover and Jaguar breather membranes (SFCC_DEC2021_39): 🟢 "Please do not order the full breather cover assembly (LR164405/AJ814231), please order the Lower-Level Repair Kit (LR166809/AJ814239)"
• Mazda 2009-2010 Tribute (01-007/13): 🟢 the throttle body is replaced only when P2135 is present; without it the answer is "No - Procedure does not apply."
• Toyota (T-TT-0362-15): 🟢 cleaning is allowed, with a limit: "Do not spray cleaning chemicals directly into the throttle body."
• Audi 2025 S5 and SQ5 (2078915/1): 🟢 "Do not replace any components for this condition", because it "will not resolve the customer's concern."
• Mitsubishi 2014-2015 Mirage (TSB-15-13-001 and its revisions): 🟢 for a PCV hose that came off, "Only replace the hose if it is damaged."

The 10-minute check

1. Write down when it happens (2 minutes). Cold or warm? Air conditioner on? Only at a stop, only in Drive, only after highway driving? Did it start after a battery change, a throttle cleaning, a car wash or a software update?

2. Read every code, with freeze frame (2 minutes). In most papers P0506 appears inside a list of codes, so read every code. 🟢 With P0299, P0101, P0172 or P1101 on a GM 1.5L turbo, GM starts at the boost pipe; with P0106 on a V8 truck, at a valve spring (the P0106 guide); with P2111 or P2135, at the throttle body; with P2172 in the 2020 Wrangler flash, the printed cause is engine software, not a leak. Lean codes: P0171; airflow codes: P0101, P0103.

3. Look at the air path (3 minutes). Engine off and cool: is the pipe or boot between the air filter and the throttle body seated and clamped, are the intake hoses on, is anything cracked? 🟢 GM's first step for the 1.5L is to confirm the connection of the charge air cooler outlet pipe at the throttle body.

4. Think back and check the battery (2 minutes). Battery disconnected or replaced, throttle cleaned, computer updated? That is Route 3. A weak battery can matter: 🟢 Audi's 2025 S5 and SQ5 P050600 paper names a low 48-volt and 12-volt charge as the trigger, though Audi says that follows long stationary periods, not normal driving. A parts store tests a battery free (how to test one); the voltages makers ask for during a relearn or a flash are the shop's job.

5. Run the VIN (1 minute). At nhtsa.gov/recalls, and with a dealer for bulletins, campaigns, software updates and emission recalls, which may not show up there.

Seven P0505 and P0506 situations, and which is yours

"A 2018-2022 Equinox, Malibu or Terrain 1.5L that loses power, runs rough or nearly stalls, with P0506, P0299 or P0101." The boost pipe (the free recall is 2019 only). → Routes 1 and 2.

"A 2026 Palisade Hybrid with P050500 or P050600." Software under campaign LA16. → Route 1.

"A 2026 Santa Fe or Santa Cruz 2.5T with a low idle or vibration in Drive or Reverse, or P050600." A torque converter. → Route 5.

"A Land Rover or Jaguar with a surging idle and P0505, P0506 or P0507." A plug, a diaphragm, a membrane or the timing. → Route 2.

"The idle sags or hunts after a battery change, a cleaning or a new computer." The relearn. → Route 3.

"A Lexus 2UR-GSE V8 with P0505 or P2111, or any car with a throttle code and a sticky idle." → Route 4.

"The car dies when I stop, there is no code, or there is a misfire and an engine noise." Software first, then mechanical causes. → Routes 1 and 5.

The P0505 and P0506 price ladder, from the bottom up

How much does it cost to fix P0505 or P0506 in 2026, and when is the throttle body the wrong first purchase? PulsCar took every dollar figure in the 1,015 complaints that an owner tied to a repair, test or tow for this fault: 37 figures in 33 complaints, 22 of them bills or amounts paid. A diagnostic fee runs $100 to $967 with a median of $123, an idle valve $150 to $800, throttle body work $100 to $1,300, an engine computer $800 to $1,400 and a leak repair $300 to $2,000. Our guides carry $15 for a throttle cleaning yourself, $80 to $150 at a shop, $150 to $300 for an idle valve and $300 to $800 for an electronic throttle body. A recall or warranty repair costs $0, so the software level, the air path and the VIN come before any part.

The five routes, cheapest first

Each route is a place the idle can be lost, starved or misjudged, ordered by what it costs to rule out and how often the documents print it. "Came back" means the owner says the same fault returned. Fuel, ignition or engine mechanics is the most-named cause (93 of the 221 that name one, 42%) but sits last, because it is the least specific and costs the most to get wrong; the papers put software, the air path and the throttle body first. The idle valve is where 11 complaints end, and no paper names it as the cure for a low idle.

Route 1 · A free repair: software, a recall or special coverage — $0 when it applies

What it is. The maker has printed a fix for a low, hunting or stalling idle on certain cars: usually a software update, sometimes a small part, paid by warranty, a campaign or a recall. The status of each is in the coverage file below.

What the documents say.

• 🟢 GM 1.5L turbo (Equinox, Terrain, Malibu): 22-NA-224 lists "P0506: Idle Speed Low" among five codes with the cause "This condition may be caused by the Charge Air Cooler (CAC) outlet tube to throttle body connection has become separated."; dealers install a retainer kit, 0.4 hour. The emission recall N192271200 (2019 models, about 170,000 vehicles) says "When the vehicle reaches low speed or idle, the engine could stall." and is free "regardless of mileage, age of vehicle, or ownership, from this time forward." The P0299 guide covers the pipe's dealer-inventory update (N192266090, expired); the owners' recall above is the open one.
• 🟢 Hyundai 2026 Palisade Hybrid, built 08/11/2025 to 09/30/2025: campaign LA16: "may set DTC P050500/P050600." The repair is an engine software update, 0.3 hour, "within 8 / 80,000 Emissions Warranty".
• 🟢 Audi 2025 S5 and SQ5: 2078915/1: "There is a software deviation in the engine control and HCP1, resulting in fault P050600 being stored in the engine control unit." (HCP1 is Audi's main control unit for the drive and running gear systems.) Revision 2079911/4, dated September 25, 2026, names the trigger: starting the engine with the 48-volt battery below 28% charge and the 12-volt battery below 12.0 volts. Audi says this does not occur in normal vehicle operation but typically after extended stationary periods in transport or at the workshop. It says the update "has already been rolled out."
• 🟢 Stellantis flashes with P0506 in a list. The 2020 Wrangler 2.0L papers add P2172, a vacuum-leak code, and print "CAUSE: PCM Software." (18-070-23, 0.3 hour). The 6.7L Cummins Ram flashes list "P0506-00-Idle Control System Rpm - Lower Than Expected." with "Unstable idle when AC compressor cycles." (18-055-22); the 2019 Ram 2500 and 3500 paper adds "Tachometer bouncing at idle with no change in RPM." and requires recall Y78 first (18-101-22 Rev. A). The ProMaster City and Ram 1500 eTorque flashes are in the P0507 guide.
• 🟢 Software for the same feel, no code: Scion FR-S and Subaru BRZ (transmission computer, S-SB-0021-15, 16-96-15); BMW N55 ("Unfavorable DME software", SI B12 15 14); Mercedes M254, where version 4 (December 2025) gives a software fix for Model 206 cars of model years 2022 and 2023 after version 1 said "Do not replace parts or perform control unit software updates/adaptations." (LI07.70-P-078547); Nissan 2020 Kicks, "ENGINE STOPS RUNNING WHEN COMING TO A STOP" when no light is on and no code is stored, fixed by a reprogram and an idle air volume learn (NTB20-028).
• 🟢 Three Nissan recalls for a stall at idle that are not about the idle valve. Juke 11V-583 (2011): a separated air inlet tube puts the car in fail-safe mode with the lamp on, and "If the vehicle continues to be driven in this condition without being promptly serviced, it could eventually stall while idling increasing the risk of a crash." Nissan's letter adds: if the check engine lamp is lit, contact the dealer immediately. Quest 12V-076: on a decline with about ¼ tank or less the engine may stall without the low fuel warning lamp (fuel pump software, then a relearn). Infiniti M 13V-430 (2006-2010 M35 and M45): an accelerator pedal sensor fault puts the engine in limp-home mode, and "This condition, when combined with restricted air flow due to deposits at the throttle valve, in rare instances, may cause the engine to stop running at idle or just before stopping." The engine can be restarted; the fix is a new pedal assembly and a reprogram.

What the owners report. 115 of the 1,015 complaints mention a recall, campaign or bulletin about this problem (11%), and 32 of those say the problem came back. A 2015 Colorado owner's dealer read P0506 with no light on, could not repeat a stall pulling away from a red light, and "DECLARED VEHICLE SAFE TO DRIVE"; it stalled again at a two-way stop.

The cheap cause that gets skipped. The software level and the VIN. A dealer can compare the software with the latest and run the VIN against open campaigns; on the cars above that is the repair, free where a recall or program covers the car, otherwise a warranty or paid repair.

Fix it yourself. The lookup only. A flash needs the maker's tool and a charger that holds the voltage (Stellantis wants 13.2 to 13.5 volts). nhtsa.gov/recalls lists safety recalls; campaigns, updates and emission recalls need the dealer and your VIN (our advice: do not wait for a letter).

At the shop — say this: "Please run my VIN for any recall, campaign, special coverage or software update that names a low, unstable or stalling idle, P0505 or P0506 on this engine, and write the answer on the repair order before any part is ordered."

Route 2 · The air path: a pipe, a plug, a hose, a ventilation part — $10 to $100 for a hose, $50 to $150 for a smoke test; owners report $300 to $2,000 for leak repairs

What it is. Air that reaches the engine without being metered, or fails to reach it. At idle the throttle is almost shut, so a small leak is a large share of the air; that is why P0505, P0506 and P0507 turn up in the same papers.

What the documents say.

• 🟢 Land Rover LR2 (2013) and Range Rover Evoque (2012-2013): LTB00606NAS1, "Engine MIL Illuminated with DTC P0505-8F and P2282-00 Stored and Misfire"; "This may be caused by the intake manifold vacuum plug having fallen out." The fix is a plug kit and a tie strap, 0.1 hour.
• 🟢 Land Rover (V6 and V8 petrol engines) and Jaguar: SSM74374 and SSM74375: "Any of the following DTCs (indicating an air intake system leak) could be stored in the Powertrain Control Module (PCM) - P2187, P2189, P0505, P0507." The cause is a ruptured camshaft cover diaphragm and the repair is a kit, not the whole cover. For the 2019-2022 AJ20-P6 engines, SFCC_DEC2021_39 lists P0505, P0506 and P0507 with the do-not-order line quoted above (the P0507 guide has the rest); the earlier sheet SFCC_SEP2021_34 said the only repair was the whole breather cover, so read the date on the sheet your shop uses.
• 🟢 GM intake manifold bolts (LCV, LKW and LTG engines, 2013-2017): PIP5529B lists P0506 among ten codes, "In rare cases, some customers may comment that the malfunction indicator lamp is on, vehicle has a hesitation or may stall." and says: "If service information does not lead to a solution, inspect the intake manifold bolts for being loose." The labor is 0.4 hour.
• 🟢 GM 2014 Impala, 2.5L: PI1203B: "the vehicle runs rough or engine stalls and may illuminate the MIL and have set DTC P0506." The cause is "water vapor getting ingested into the induction system through the air intake that is located behind the grille" after a car wash; the repair is a revised air deflector, 1.1 hours.
• 🟢 Toyota 2007-2011 Camry Hybrid: T-SB-0012-16 pairs P2111 with "possible engine stall condition while the vehicle is stopped" and replaces the PCV valve.

What the owners report. Nine of the 1,015 complaints end at an air leak (1%), and five describe a stall. A 2014 Ram 1500 owner: "THE IDLE DROPPED TO 550 RPM S (REVOLUTIONS PER MINUTE) WHICH SHOULD BE 900 RPM AND THE ENGINE STALLED OUT."; a Buick Cascada owner whose low, rough idle was traced to a leaking PCV in the camshaft cover puts the repair at $1,800 to $2,000.

The cheap cause that gets skipped. The connection at the throttle body, a clamp or a boot, and the manifold bolts. Ten minutes of looking costs nothing; re-tightening the bolts is 0.4 hour of labor, a fraction of a throttle body's $300 to $800.

Fix it yourself. Look and listen: with the engine off and cool, check that the pipe or boot between the air filter and the throttle body is seated and clamped and that vacuum hoses are on; with the engine idling, listen for a hiss. Do not torque manifold bolts by feel; GM's paper prints no torque value (our advice: use the manual). A smoke test is shop work, $50 to $150 in our idle-shaking guide.

At the shop — say this: "Before a throttle body or an idle valve, can you check the pipe and boot connections at the throttle body, smoke-test the intake, check the crankcase ventilation and show me the fuel trims at idle?"

Route 3 · Clean the throttle body and relearn the idle — $15 yourself, $80 to $150 at a shop

What it is. The computer learns how far the throttle must open to hold the idle. Carbon, a disconnected battery, a cleaning or a new or reflashed computer can leave the learned value wrong, and the idle sags, hunts or dies until it is relearned. The P0507 guide carries the GM and Nissan procedures.

What the documents say.

• 🟢 GM 2002-2009 Trailblazer and Envoy (Rainier 2004-2008, Bravada 2002-2004, Saab 9-7X 2005-2008): PIT3116B: "Engine may stall with the air-conditioner on and or while adding additional loads to the engine at idle." and "This concern may not set any diagnostic trouble codes." The fix is to clean the throttle bore and plate with a shop towel and GM top engine cleaner.
• 🟢 GM V8s, 2006-2018: PIP4578B ties P0506 and P0507 to a throttle that was cleaned without the idle learn: "If carbon is present, follow the Throttle Body Cleaning Procedure in SI to clean the throttle body."
• 🟢 Toyota, many 1998-2012 models with electronic throttle control: T-TT-0362-15 for an "abnormally low or rough idle after the battery has been disconnected": "Inspect the throttle body for excessive deposits.", clean with a rag, and "allow the engine to idle for at least 3 minutes after reaching full operating temperature."
• 🟢 Two relearn papers that are not low-idle ones. Acura 2015 TLX V6 (hesitates, surges, idles high): 15-038: "The idle learn is unable to relearn its parameters when the CAN system is interrupted during an ECM, TCM, or control unit update." Honda 2016 Pilot: A15110F, for transmission code P2638: "Chances are the idle learn procedure wasn't done right at PDI." (PDI is the dealer's pre-delivery inspection.)

What the owners report. 86 of the 1,015 complaints mention a throttle body cleaning (8%), and 60 of those say the problem came back; 26 mention a relearn, and 21 of those say the same. Owners who write about cleanings are often writing about a second visit, so read those shares as histories, not a failure rate. A 2004 Camry owner cleaned a gummed-up throttle with foaming cleaner and wrote: "COMPUTER CANNOT UNDERSTAND NEW THROTTLE POSITION AFTER CLEANING, ENGINE SURGES FROM ABOUT 800 RPM TO ABOUT 3000 RPM IN IDLE." (Toyota's tip says not to spray cleaner into the throttle body.)

The cheap cause that gets skipped. The history: a battery change, a cleaning, an update or a new computer in the weeks before the idle changed.

Fix it yourself — the honest split. Cleaning the throttle on an engine-off, cool car, with the cleaner on a rag and nothing sprayed into the bore, is a driveway job on many cars; the relearn often is not, because on GM, Honda and Nissan cars it is a scan-tool procedure with conditions (Nissan wants more than 12.9 volts at idle and a warm engine). If the idle is wrong after your cleaning, the relearn is the first thing to do, not a new throttle body; ask what it costs before you agree to it (our advice).

At the shop — say this: "The battery was disconnected, the throttle was cleaned, or the computer was updated before this started. Can you run the maker's idle relearn and show me the learned idle values before and after, before we talk about parts?"

Route 4 · The throttle body or idle valve, replaced — $300 to $800 for a throttle body, $150 to $300 for an idle valve

What it is. The part that meters idle air is worn, sticking or failing: a throttle plate that sticks, an electronic throttle motor that fails, or on older engines an idle air control valve. A quote can start with a throttle body; the makers' papers do the opposite. They replace one late, or only when a throttle code such as P2111 or P2135 is also stored (the Lexus V8s are the exception), and no paper replaces an idle valve for a low idle.

What the documents say.

• 🟢 Lexus 2UR-GSE V8s (2008-2014 IS F, 2015-2025 RC F, 2016-2020 GS F, 2018-2025 LC 500, 2021-2025 LC 500c, 2022-2025 IS 500): L-SB-0032-25, July 2025: "P0505 - Idle Control System" with P2111. "The throttle body assembly with motor and ventilation hoses no. 2 and no. 3 have been modified to address these conditions." The labor is 1.3 to 1.8 hours, the paper prints no idle relearn step, and it applies only to cars built before the printed VINs, with the code present.
• 🟢 Mazda 2009-2010 Tribute built 6/22/2009 to 10/15/2009: 01-007/13: "Drivability symptoms may include intermittent rough idle, idle speed below specification and/or reduced power." The throttle body is replaced only when P2135 is present, 0.6 hour.
• 🟢 The idle air control valve. No paper in the set tells a shop to replace one on a car or truck for a low or unstable idle. Mazda's multi-model repair tip does say to replace a stuck-open valve, for a high idle: "If the IAC valve is stuck open, replace it to correct customers concern."

What the owners report. 31 complaints end at a throttle body (3% of the 1,015; 14% of the 221 that name a cause), 20 of them Fords; 15 describe a stall and 11 say it came back. 11 end at an idle valve, one with a stall. A 2001 Infiniti I30 owner paid $800 for an idle control valve that did not help, was then told the throttle control body was the problem and paid $1,300 for it, and was next quoted $3,900 for motor mounts.

The cheap cause that gets skipped. The cleaning and relearn of Route 3, the software of Route 1 and, for an electronic throttle, the connector and the codes (P2111, P2112 and P2135 point at the throttle; a bare P0505 or P0506 does not, except on the Lexus V8s).

Fix it yourself — the honest split. On many four-cylinder engines the throttle body is a few bolts, a gasket and a connector; the swap is within reach, the idle relearn is not without a scan tool. On the Lexus V8s it is a dealer job.

At the shop — say this: "What test shows the throttle body or the idle valve is at fault, not dirty and not mis-learned? Did you clean and relearn first, is there a bulletin for my VIN, and what does the part cost without the labor?"

Route 5 · Deeper causes that mimic it: engine mechanics, a torque converter, a purge valve, a sensor — from $0 to thousands

What it is. The idle code is the last link. An engine that cannot make steady power (a broken valve spring, a leaking purge valve, a bad sensor reading), a transmission that drags at a stop, or engine-mount vibration that feels like a low idle all set or imitate the same complaint.

What the documents say.

• 🟢 Valve springs (GM V8 trucks, Camaro, Corvette, CTS-V): PIP5423 for a lamp with P0106 and P0506: "This maybe caused by a broken valve spring". The P0106 guide has that route.
• 🟢 Hyundai 2026 Santa Fe and Santa Cruz 2.5T: 26-AT-003H for "LOW IDLE OR EXCESSIVE VIBRATION DTC P050600": "caused by the one-way clutch sprags being misaligned." (That clutch is inside the torque converter, the coupling between engine and transmission.) The repair takes the transaxle out, 4.7 hours (2WD) or 4.9 hours (4WD), and only after the dealer confirms the symptom; terms are in the coverage file.
• 🟢 Subaru 2010-2012 Legacy and Outback CVT: 16-90-13 "to address a customer concern of very low engine RPM when coming to a stop." Worn thrust washers inside the torque converter can leave its lock-up clutch, which ties the engine to the wheels, releasing late or not at all as the car stops; the paper says "Perform a line pressure test to rule out other possible pressure-related causes for the condition."
• 🟢 GM purge valve special coverages (for example N232395300, 2019 Enclave and Traverse, 2020 Encore, Sonic and Trax): "the engine could run rough, hesitate, or stall at idle speeds." The valve is replaced only if the diagnostics lead to it. Toyota RAV4, 2022-2025: 26TC03: steam on the radiator can give a wrong airflow reading, leading to "a potential engine stall while idling or operating at low speeds."
• 🟢 Timing and block: a Land Rover and Jaguar 2.0L that surges after a timing cover repair, with P0505 ("The mechanical timing of the engine needs to be confirmed as correct.", SFCC_MAY2020_27); a 2023 Honda CR-V Hybrid whose engine block was machined wrongly at the crankshaft sensor mount, with a low-speed rough idle and rpm hunting among the symptoms (A23-049). GM 2019-2021 Silverado and Sierra PIP5798: a rough idle that "may be described as a low idle", with "Wrong fuel used (regular instead of premium when required)" among the causes.

What the owners report. 93 complaints end at fuel, ignition or engine mechanics (9% of 1,015, 42% of the 221 that name a cause): 35 mention a valve, a camshaft or timing, 18 the fuel pump, pressure or filter, 9 plugs or coils. 48 end at another named cause, and 13 of them mention a torque converter, a lock-up or a CVT; of the 53 Subaru complaints, 10 cite 16-90-13. A 2011 Subaru Outback owner: "IT ALSO STALLS WHILE APPLYING THE BRAKE TO STOP AT A LIGHT ON A HILL." And 80 complaints (8%) end with a shop that found nothing: 46 of those describe a stall and 29 say it came back.

The cheap cause that gets skipped. The cheaper test that rules the expensive part in or out: a line pressure test before a converter, a cylinder leakage test before a head, a smoke test before a gasket, the fuel grade the manual asks for. Ask what a test costs before the price of the part.

Fix it yourself. Only the free ones: use the fuel grade your manual asks for, and do not fill the tank with the engine running (our advice; GM's police Tahoe sheet, PIP5172B, says drivability concerns "can be induced by fueling with vehicles running"). Everything else on this route is shop work.

At the shop — say this: "The idle code has no part on it. What did you test to rule out the air path, the software, the fuel and the engine, and what does the test for the part you want to sell me look like?"

The coverage file: which recalls and programs run in September 2026

The status column is our computation from the printed terms, as of September 2026, not a promise from any maker. Most of these papers print no end date, and the VIN decides. Bulletins that print only "reimbursable within the provisions of the warranty" are ordinary warranty repairs and are not listed.

Campaigns, updates and emission recalls are not in the safety-recall lookup: nhtsa.gov/recalls may show nothing for them (GM's N192271200 and Honda's 23-049 are emission recalls), so the dealer, with your VIN, is the lookup.

What 2,200 complaints show

How we went through them. We took every NHTSA owner complaint received from January 2015 through early October 2026 that names these codes, uses idle-control wording or describes an idle that hunts, sags or dips: 2,200 in all. Each was sorted twice, independently, by the same written rules. The sorting rules and how we did it are published. 1,015 describe a low, hunting or stalling idle or an idle-control repair; 1,185 do not. Complaints that say only "stalls" or "rough idle" were left out by rule (6,132, listed in a published file), so the stall share describes this set, not all stalls.

What the owners describe. 526 describe a stall (52%; the set was chosen by idle and stall wording, so this is not how often the codes lead to one), 283 an idle that hunts or surges (28%), 164 a low or rough idle (16%) and 42 only a code or a repair (4%). Of the 221 that name a cause, fuel, ignition or engine mechanics is 42%, another named cause 22%, the throttle body 14%, a sensor 7%, the computer 6%, the idle valve 5% and a leak 4%. 115 mention a recall, campaign or bulletin about the problem (11%), 285 a problem that came back (28%) and 26 a relearn (3%).

The 23 that print the code. 7 print P0505 and 17 print P0506, one of them both. Two are one 2017 GMC Yukon XL owner's account filed twice.

Is a stalling idle dangerous, and does a new throttle body or idle valve stop it? PulsCar counted what 1,015 federal owner complaints say about an idle problem: 526 describe a stall (52%, in a set chosen by idle wording), 229 of those mention a stop sign, a light or an intersection, and NHTSA marks 7 of the 1,015 as a crash, one as a fire and six as a tow. Where a complaint ends at a throttle body, 11 of 31 say the problem returned; where a shop found nothing, 29 of 80. No document that prints P0505 or P0506 says to stop driving, though GM's P0506 recall warns of a stall at low speed or idle; the one do-not-drive wording we found is an Infiniti recall letter that prints neither code. Our rule: an engine that dies at a stop or while rolling is a tow, not a drive to the shop; rule out software and air first.

When the engine dies: the safety side

Of the 526 stall complaints, 229 mention a stop sign, a light or an intersection (44%), 42 the steering (8%) and 70 the brakes (13%); 100 mention a highway, freeway or interstate (19%), 45 say "without warning" or "no warning" (9%) and 158 mention restarting the engine (30%). In NHTSA's own fields, 7 of the 1,015 are marked as a crash, one as a fire, none with an injury or a death, and 6 as towed. A 2016 Explorer owner: "DRIVING ON FREEWAY AT 65MPH. CAR STALLED LEAVING NO POWER TO STEERING AND BRAKES." (A stall at speed, not at idle.) 🟢 Nissan's Juke recall, above, warns of a stall and a risk of a crash if the car is kept in use without prompt service. On the other side, NHTSA's closing summary for a 2012 petition about Ford throttle bodies says "Vehicles are not likely to unexpectedly stall as a result of this condition, but drivers may characterize the reduced functionality as a stall". A stall in a moving car is a safety fault; a limp mode that drops the revs is another thing.

What owners say they paid

37 figures in 33 of the 1,015 complaints are ones an owner tied to a repair, test or tow for this fault: 9 amounts paid, 13 bills and 15 quotes. They are what owners wrote, not audited invoices, and we publish them with NHTSA complaint numbers.

Why P0505 and P0506 come back after a repair

The part was not the cause: a new throttle body on an air leak, a new idle valve that did not help (a 2001 I30 owner paid $800, then was told it was the throttle body, then the mounts), a cleaning on a software fault. The relearn was skipped or did not hold: 21 of the 26 complaints that mention a relearn say the problem returned. The cause is intermittent: the 2015 Colorado dealer could not repeat the stall, and Hyundai's torque converter bulletin demands that the dealer confirm the symptom first. The fix came later: Mercedes's M254 bulletin went from "do not replace parts" to a software fix in its fourth version (Model 206, 2022-2023 only), and Toyota's RAV4 campaign offers a free radiator air guide while its software alternative is still being developed.

Can you drive with P0505 or P0506?

It depends on whether the engine stays running, and this is our rule, not any maker's. None of the papers that print P0505 or P0506 tells the owner to stop driving: Audi calls its 2025 P050600 concern one that "does not occur during normal vehicle operation", though GM's 2019 1.5L recall that lists P0506 warns that the engine could stall at low speed or idle. The strongest wording is on a neighbouring recall: Infiniti's interim owner letter for the M35 and M45, whose engine may stop when coming to a stop, says "Do not continue using your vehicle with the MIL illuminated." (MIL is the check engine light; the letter belongs to that recall, and for any car whose engine has died our rule is as strict.) A steady light and an idle that wanders but never quits: a shop within days, and do not clear the code first; on a recalled Nissan Juke or Infiniti M with the lamp lit, the dealer immediately, as their letters say. An engine that dies at stops, when slowing down or while rolling, or that dies and restarts roughly: have it towed, not driven to the shop, and do not use it for ordinary trips until it is diagnosed. If the check engine light is flashing, pull over safely, switch the engine off and have it towed; for a flashing light only, the one exception is a shop within 2 to 3 miles, reached gently, under 40 mph with light throttle (our advice). If the engine dies on the road (our advice): hazard lights, steer to the first safe place with the momentum you have, shift to Neutral, restart only to clear the road, then call for a tow. The steering and brakes may get heavy or lose assist without engine power, which 42 (steering) and 70 (brakes) of the 526 stall complaints mention; the stall-while-driving, shaking at idle, vibration at idle and running rough pages cover the neighbours.

Should you buy a used car with a P0505 or P0506 history?

Ask what was found, not what was replaced: 29 of the 80 complaints that end with a shop finding nothing say the problem returned. Ask for the invoice that names the test (software level, smoke test, relearn), have a dealer run the VIN for the recalls above, and before you pay let the car warm up fully, then sit at a stop with the air conditioner on, in Drive and in Park, watching the tachometer.

Clearing P0505 or P0506 before an inspection

A cleared code returns if the cause is still there, and many inspections need the car's self-checks to have run again after a clear; ask the station how many trips it needs. Fix first, drive several normal trips, then test; how to reset a check engine light covers the mechanics.

What the papers tell a shop to do with a low idle, checkpoint by checkpoint

1 · The code and the conditions: every code with the freeze frame, and when it happens. 2 · The software: the level and any bulletin number; on a Stellantis, Hyundai, Audi or Mercedes the repair may be only this. 3 · The air path: the pipe or boot at the throttle body, the manifold bolts, the ventilation parts, a smoke test. 4 · The throttle: clean it the maker's way and relearn the idle. 5 · The VIN: recalls, campaigns and special coverages. 6 · The part: only then a throttle body, a sensor or a computer, with the maker's relearn.

Three P0505 and P0506 traps

Trap 1 · Buying an idle valve or a throttle body from the code. No paper tells a shop to replace an idle air control valve for a low idle, and GM and Mazda put conditions on the throttle body (see the do-not-replace lines).

Trap 2 · A cleaning or a battery change with no relearn. 86 complaints mention a throttle body cleaning and 60 say the problem came back; 21 of the 26 that mention a relearn say the same. GM puts a learn after a cleaning or a new or reprogrammed computer; Acura, Nissan and Infiniti after a reprogram; Honda after delivery prep.

Trap 3 · A cleared code or "could not duplicate" taken as a repair. 80 complaints end with a shop that found nothing, and 29 say it came back. Ask for the freeze frame and the software level on the repair order, not a clear.

The P0505 and P0506 plan: 10 minutes, today, this week

Today (10 minutes). Key off, look at the pipe or boot at the throttle body and the intake hoses, write down when the idle goes wrong and whether anything changed first, and read the code (a parts store reads it free; ask for the freeze frame, and if their scanner cannot show it the shop will). Today (VIN). Ask a dealer for recalls, campaigns and software updates by number. This week. If the idle still wanders, pay for one diagnosis and ask for the software level, a smoke test and the throttle body check with a relearn, in that order. If the engine dies at stops or while rolling, do not drive it to the shop: have it towed. If the check engine light is flashing, pull over safely, switch the engine off and have it towed (the one exception: a shop within 2 to 3 miles, reached gently, under 40 mph with light throttle). In those two cases, act today, not this week.

These are composite scenarios, not individual customers; the dollar figures are shop-price ranges from our guides. A 2019 Equinox 1.5L loses power and nearly stalls with P0506 and P0299: the owner asks the dealer to check the pipe at the throttle body and run the VIN for recall N192271200 before agreeing to a throttle body at $300 to $800. A sedan's idle sags and hunts after a new battery and a throttle cleaning: the owner asks for the idle relearn first, before an idle valve at $150 to $300 or a throttle body at $300 to $800. A 2011 Subaru Outback with a CVT dies when braking to a stop with no code: the owner asks for a line pressure test, a check of bulletin 16-90-13 and a diagnosis at $80 to $150 before anyone sells a throttle body.

Sources and documents

Primary documents only. Claims marked 🟢 rest on one of the items below; claims marked ⚪ are shop-price estimates carried from PulsCar's repair guides.

1. General Motors: PIP5651C, PIP5651D, 22-NA-224, N192271200, N192266090 rev. 02, PIP5423, PIP5529, PIP5529A, PIP5529B, PI1203B, PIP4578B, PIT3116B, PIP5798, PIP5172B, 18-NA-328, N232395300, N192210240.
2. Stellantis: 18-008-16 Rev. B, 18-063-17 Rev. A, 18-013-20 Rev. B, 18-053-22 Rev. A, 18-070-23, 08-037-21, 18-055-22, 18-101-22 Rev. A, 18-025-26 Rev. B, 18-023-16 Rev. D, 18-052-16 Rev. A.
3. Hyundai, Kia: 26-01-021H, 26-AT-003H, 21-01-044H, Kia P050A bulletin.
4. Toyota, Lexus, Scion, Subaru, Mazda: Lexus L-SB-0032-25; Toyota T-TT-0362-15, T-SB-0012-16, 26TC03; Scion S-SB-0021-15; Subaru 16-96-15, 16-90-13; Mazda 01-007/13 and the multi-model idle air control repair tip (10076908).
5. Honda, Acura, Nissan, Infiniti, Pagani: Honda A15110F, A23-049; Acura 15-038; Nissan NTB20-028, ITB11-018b; recalls 11V-583, 12V-076, 13V-430 and Pagani's Huayra recall 18V-175, a battery software fault that can stop the engine at idle.
6. Land Rover, Jaguar: LTB00606NAS1, SSM74374, SSM74375, SFCC_MAY2020_27, SFCC_SEP2021_34, SFCC_DEC2021_39, JTB00532NAS1, Jaguar H302 NAS20.09.008.
7. Audi, BMW, Mercedes-Benz, Mitsubishi, Ford, Volkswagen: Audi 2078915/1, 2079911/4; BMW SI B12 15 14; Mercedes LI07.70-P-078547, version 1, version 3 and version 4; Mitsubishi TSB-15-13-001; Ford SSM 50548; Volkswagen 24FD.
8. NHTSA investigation summaries: DP12-006, PE13-003, PE05-027, PE03-059, PE12-016, EA08-005 and DP19-003, as listed in the document file.

Data and method: complaints, amounts, documents, the sorting rules and how we did it (CC BY 4.0).

Neighbouring pages: P0507, throttle body replacement cost, shaking at idle, vibration at idle, stalling while driving, running rough, P0171, P0101, P0103, P0106, P0299 and the check engine light.

For P0505 and P0506 the evidence is the code, the freeze frame, the software level and a look at the air path; a code read alone is not a diagnosis.

Prices verified July to October 2026 in the repair guides they are carried from and in the owner reports above, and reviewed quarterly. Technical documents verified October 2026: the 341 distinct documents in our published file, of which 240 were read in full.

Did P0505 or P0506 clear with software, a pipe, a relearn or a recall? Email [email protected] with the vehicle, mileage and outcome.