SORTING RULES - UNSTABLE, LOW OR STALLING IDLE / IDLE-CONTROL COMPLAINTS (P0505 IDLE CONTROL SYSTEM MALFUNCTION, WITH THE SISTER CODE P0506 IDLE CONTROL RPM LOWER THAN EXPECTED) PulsCar analysis of NHTSA public data, October 2026. License: CC BY 4.0 Fingerprint of the rules text below, taken when it was written and before any complaint was sorted: dd15ec4f5e74ff446444adc3c1ec7fafb80c54ae18f317b81ce4b8afdebd641e (2026-10-27T09:44:22Z) Written before any complaint in the set was sorted. ## Pool (how the complaints were found) NHTSA complaints received 2015-01-01 to 2026-10-04 (782,908 narratives; 2026-10-04 is the latest received date in the flat files). A complaint is in the pool if its narrative matches any of the following case-insensitive text searches: 1. R1 - the code P0505 or P0506 by any spelling (letter O for zero, a space, hyphen or period after the P, suffix 00), or the bare number after a code word: `(? U. - R2 a part named as the cause by a shop, dealer or mechanic, or replaced/cleaned, is the category when it is the repair stated as fixing the idle, or the last cause named. A part replaced that the narrative says did NOT fix it is not the cause. - R3 a shop or dealer that tests and finds nothing, or cannot duplicate the fault, with no part named -> K; an owner's own test that finds nothing is not K (-> U). - R4 stall = yes only when the narrative says the engine stalled, shut off, cut out or died because of the idle fault (at idle, at a stop, or rolling to a stop); a stall at speed with no idle wording, or a generic "may stall", is no. - R5 symptom: S if a stall is described (even with hunting or low idle also described); otherwise H for rpm rising and falling, surging, bouncing, hunting; otherwise L for rpm sitting or dropping too low, shuddering or nearly dying; X when no idle symptom is described (only a code, repair or bulletin). - R6 recall = yes only when a recall, TSB, service bulletin, special coverage, warranty extension or customer-satisfaction program for THIS fault is named as performed, offered, seen, asked about or refused; an unrelated recall or a generic "known issue" with no program named is no. - R7 returned = yes only when a repair, reset, cleaning or part replacement was done and the same fault came back or the owner says it did not fix it; repeated episodes before any repair are not returned. - R8 relearn = yes only when the narrative itself mentions an idle relearn / throttle learn / reset / adaptation procedure being done, skipped, needed or not performed. - R9 when the final category is N all flags are no and the symptom is X; a flag difference on an N complaint is settled as no. - R10 an excerpt that does not settle a field: choose the narrower reading (flag no; category U). - R11a vibration, shaking or shudder at idle with no stated rpm instability (no hunting, no low or dropping rpm) and no idle-control system diagnosed -> N. A cause merely listed as "possible" by the owner is not a diagnosis. - R12a rough idle or misfire assigned to a misfire / mechanical fault with the idle-control system never named and no rpm instability stated -> N. - R13a rpm that only RISES (high idle), a lunge/surge forward of the vehicle, or a runaway/launch on release of the pedal, with no low, hunting or stalling idle -> N (symptom X). A surge at slow speed while moving is not an idle surge. - R14a stall, surge or power loss while moving, pulling away, at cruise or at speed, with no idle wording -> N (symptom X, stall no). - R15a throttle body, relearn, adaptation or software mentioned with no idle complaint stated in the excerpt -> N (flags no per R9). - R16a a low, hunting or stalling idle whose cause a shop/dealer names or repairs keeps that cause's letter, including O for transmission or electrical load; N is for vibration/rough/misfire-only complaints (R11a, R12a). - R17a auto idle-stop (start-stop) system faults are not idle-control unless an idle-control part or unstable rpm is named; the cause only named as a sensor of that system -> N. - R18a "rough", "bumpy" or "uneven" idle with no stated rpm direction -> H; L only when the rpm is said to be low, slow, dropping, shuddering or nearly dying. - R19a when both hunting and a near-stall drop are described (no actual stall) -> L (the more severe), as S outranks both. - R20a three-wheeled motorcycle-class vehicles (Can-Am Spyder) are in the motorcycle exclusion -> N. - R11b vibration, shaking, shuddering, trembling or "rough idle" at idle with no rpm, hunting, low-idle, dying or stall wording and no idle-control part or code named -> N (not an idle-control fault in the low/unstable direction). - R12b relevance that rests only on an ambiguous word, or on one idle-control part inside a long parts list for another failure (turbo, limp mode, relearn after battery work), or on a stall while driving plus a throttle cleaning with no idle wording -> N. Idle-control parts swapped to diagnose the owner's own problem stay relevant (U). - R13b throttle body and idle air control named together as one defective assembly -> T. - R14b a repair that cured the fault for a stated time (days or longer) and was followed by a recurrence keeps its category (it did cure it for that time) and the recurrence sets returned=yes; a repair with no stated period of relief followed by recurrence is not the cause (U). - R15b a relevant idle described only as rough, sputtering, shaking or shuddering, with no rpm rising and falling, no stall -> symptom L (R5 shudders). - R16b rpm that rises or hangs high (off-throttle, clutch in, throttle not closing) with no low, hunting or stalling idle -> N (high-idle side, P0507 page). - R11c vibration or shaking at idle with no rpm figure, no rpm drop, no near-stall wording and no idle-control part named -> N (not a low or unstable idle). - R12c symptom: H only when rpm rising and falling (revs, surging, hunting) is described; rough idle, sputtering, or the vehicle itself jerking/bouncing/shaking with no rpm movement -> L; a stall described -> S. - R13c a stall, rough or near-stall idle that the narrative assigns to a misfire, engine-mechanical, start-stop, electrical-power or other named non-idle fault, or a complaint about power loss at speed, with the idle-control system never named -> N. - R14c K needs a stated shop/dealer test or failure to duplicate; a dealer that merely "denies" or refuses, or a tune-up/cleaning with the owner saying the fault persists, is not K (tune-up/cleaning with the fault still present counts as returned = yes under R7). - R15c recall = yes only when the owner dealt with the maker or dealer about a named recall/campaign (asked, told VIN not included, offered, refused); a bare "Ford will not recall", "no recalls issued" or "should be a recall" -> no. - R16c a failed power-distribution module or relay box (TIPM, fuse/relay block) -> O; a turbocharger or valve-train/cam-adjuster part -> F. - R11d1 an engine that stalls when shifted into gear from a standstill counts as a stall at idle (stall yes, symptom S), consistent with the agreed Altima block. - R12d1 K needs the shop or dealer itself to test the fault or fail to duplicate it; "no codes on diagnostics" with no named tester, a dealer that checked only one component (battery), or a dealer that "cannot resolve" it -> U (R14c). - R13d1 a trouble code or warning that only appears in the narrative, with no shop, dealer or repair naming a part as the cause, is not a diagnosis -> U (R1, R10). - R14d1 a fault the owner or maker blames on the vehicle as a whole ("small engine", "the way the motor sits", "fuel tank scenario") with no part named is U. - R11d2 an engine-mechanical failure (bearing failure, oil starvation, blown gasket, engine needs replacing) with poor idle, stall or near-stall named only as a symptom and the idle-control system never named -> N (symptom X, flags no); applies R13c. - R12d2 low engine oil named by the dealer as the cause of a bucking / revving high and low engine is engine mechanical -> F; a cause cut off in a truncated excerpt, or named only by the owner in a one-line summary, is not settled -> U (R10). - R13d2 stall = yes needs a stall that the narrative ties to idle or slowing to a stop; a die-out while pulling away or accelerating, with a separate low idle described later, keeps symptom L and stall no (R4, R19a). - Note on R18a, R12c and R15b: they pulled in different directions for a rough or bumpy idle with no stated rpm direction (R18a: symptom H; R12c and R15b: symptom L). R15b and R12c were applied, so such a complaint is marked L. ============================================================================== POOL HISTORY - First search: 1,864 complaints, found by the three text searches R1, R2 and R3 above (code, idle-control wording, hunting or low-idle wording). They were sorted in 9 groups of about 200. - Plain "stalls" and "rough idle": narratives that say only that the engine stalled or idled rough, with no idle-control wording, no code and no rpm or hunting wording, were left out on purpose (thousands of them describe a misfire, a fuel fault or a transmission fault). They are listed, not sorted, in complaints-not-sorted.txt (6,132 narratives). - Completeness search (a separate search of the whole complaint file, run after the first batch was sorted): about 1,950 narratives were read, and 336 more complaints that the first search's wording could not match were found, 321 of which the sorting then counted as relevant (idle described as "idles low", rpm figures, rpm or tachometer movement without the word idle, generic idle wording, misspellings of idle). The search ran to the end of what it looked at; it was not stopped by a cap. All 336 were sorted (second batch, two groups of 168). found_by in the complaints file says which search found each complaint ("first search" or "independent check"). - Final: 2,200 complaints; 1,015 relevant, 1,185 not relevant. A relevant complaint is one that describes a low, unstable or stalling idle, or an idle-control system diagnosed for it, on the owner's vehicle. - After the settling of disagreements, a final check changed 13 rows under the same rules (12 stall marks set to yes, 1 relearn mark set to no): relevant complaints whose wording contained a stall word or a relearn word were read in full and the mark was changed where the whole text says so (the sorting had seen only a window around the matching words).