Rough idle: Codes, Causes & Fixes

A shaky or uneven idle is most often caused by a vacuum leak, a misfire from worn spark plugs or a weak ignition coil, a dirty throttle body or an EGR valve stuck partly open. Related codes include P0300–P0312, lean codes like P0171 and idle control codes like P0505. Listen for hissing around intake hoses with the engine running and note whether the idle is worse when the engine is cold or warm.

184Codes

2.7Average severity

10%High or critical

19%DIY-friendly

Severity distribution

Most viewed

P0174 Powertrain The cylinder bank without cylinder 1 is running lean even with the maximum fuel correction… Moderate P0300 Powertrain The engine computer sees misfires that jump between cylinders or hit several cylinders at once. High P0101 Powertrain The MAF sensor's airflow reading doesn't match what the engine computer expects… Low P0171 Powertrain The engine computer is adding the maximum extra fuel it's allowed on bank 1 and still sees… Moderate P0172 Powertrain The engine computer is pulling as much fuel as it's allowed on bank 1 and the mixture is still… Moderate P0302 Powertrain Cylinder 2 keeps misfiring. On inline engines it's a middle cylinder, so rule out coolant… Moderate

All codes (114)

All Severity 3+ Severity 4+

P1380 Chevrolet · Powertrain A misfire was detected, and the ABS module couldn't supply rough-road data to confirm it wasn't… Moderate P1381 Chevrolet · Powertrain A misfire was detected while the PCM had lost contact with the ABS module that supplies… Moderate P1399 Honda · Powertrain An older Honda's PCM counted misfires that jump between cylinders instead of staying in one. Moderate P1516 Chevrolet · Powertrain The electronic throttle didn't move to where the computer commanded, so the engine drops into… Moderate P1519 Honda · Powertrain The PCM found a fault in the idle air control valve (IACV) circuit on a Honda with a cable… Moderate P1603 Toyota · Powertrain Toyota's ECM logged that the engine stopped by itself while running, without the key being… Moderate P2101 Powertrain The throttle plate isn't reaching the position the computer asks for, fast enough or accurately… Moderate P2108 Powertrain The throttle control module isn't performing as expected – check its power, data link… Moderate P2111 Powertrain The throttle plate stayed more open than commanded – a real safety concern until you know why. High P2112 Powertrain The PCM asked the throttle to open, but it stayed shut – the engine can't get air, so it bogs… High P2119 Powertrain The throttle plate isn't reaching the position the PCM commands, or won't spring back to its… Moderate P2121 Powertrain The main gas pedal signal stays within normal voltage but moves in a way a real pedal can't. Moderate P2146 Powertrain The shared power feed for one group of injectors is open, so every injector in that group has… High P2149 Powertrain The shared supply to the second injector group dropped out, often an intermittent wiring fault… High P2188 Powertrain At idle, bank 1 gets extra fuel from somewhere the PCM doesn't control; above idle the mixture… Moderate P219A Powertrain One cylinder on bank 1 runs clearly richer or leaner than the others, even if the average looks… Moderate P219B Powertrain One cylinder on bank 2 runs off the mixture of the other cylinders on that side of the engine. Moderate P2647 Powertrain The VTEC oil pressure switch reports the high-lift rockers engaged while the engine computer… Moderate P3190 Toyota · Powertrain The hybrid computer asked the gas engine for power and got less than expected. Moderate P3400 Powertrain Cylinder shut-off on bank 1 (AFM, DFM, MDS or VCM) isn't doing what the engine computer… Moderate P3497 Honda · Powertrain Honda's Variable Cylinder Management on the front cylinder bank didn't behave the way the PCM… Moderate U0105 Network The PCM lost contact with the separate module that fires the injectors, common on diesel… High U0107 Network The engine computer can't reach the module that drives the electronic throttle, so power is cut… High U0115 Network Modules lost contact with the second engine computer on vehicles that use two of them. High

Symptoms

Check engine light on 558 Loss of power 214 Limp mode 165 Poor fuel economy 146 Engine stalling 133 Car won't start 123 Harsh or slipping shifts 80 ABS / traction light on 65 Fuel smell 34 Check engine light flashing 22