Rough idle: Codes, Causes & Fixes

P0174 Powertrain The cylinder bank without cylinder 1 is running lean even with the maximum fuel correction… Moderate 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 P0300 Powertrain The engine computer sees misfires that jump between cylinders or hit several cylinders at once. High P0302 Powertrain Cylinder 2 keeps misfiring. On inline engines it's a middle cylinder, so rule out coolant… Moderate

P0400 Powertrain EGR flow doesn't match what the ECU expected, and the code doesn't say whether it's too much… Low P0402 Powertrain More exhaust is being recirculated than the ECU asked for, usually because the EGR valve won't… Moderate P0403 Powertrain The ECU found an electrical fault in the circuit that drives the EGR solenoid or electric EGR… Low P0404 Powertrain The EGR valve isn't moving to the position the ECU commands, or its position report doesn't… Low P0409 Powertrain The ECM lost a usable signal from the EGR position or pressure sensor – often an open… Low P0441 Powertrain The ECU opened the purge valve but saw the wrong flow: too little, too much, or at the wrong… Low P0458 Powertrain The purge valve control line reads too low: lost power feed, open coil or a wire shorted… Low P0496 Powertrain Vapor is being drawn into the engine while purge is commanded off: almost always a purge valve… Low P0505 Powertrain The engine computer can't hold idle speed where it wants it – usually a dirty or sticking idle… Low P0506 Powertrain The engine idles below the computer's target even with idle air opened up – usually a gummed-up… Low P0507 Powertrain The engine idles faster than the computer's target – most often extra air is sneaking… Low P0508 Powertrain The idle air control circuit reads low voltage – a shorted valve coil, lost power feed or wire… Low P0509 Powertrain The ECU sees too much voltage on the idle air valve circuit, so it has lost control of the idle… Low P0511 Powertrain The computer can't drive the idle air control valve properly – typically an open winding… Low P052E Powertrain The crankcase ventilation regulator isn't controlling crankcase pressure properly – often… Moderate P0550 Powertrain The engine computer lost a believable power steering pressure switch signal; idle may dip when… Low P0560 Powertrain The engine computer saw its supply voltage missing or out of range – check fuses and feeds… Moderate P0561 Powertrain System voltage jumps up and down instead of holding steady – often loose terminals… Low P0603 Powertrain The engine computer lost its learned memory – usually after a battery disconnect or a bad… Low P0604 Powertrain The engine computer's working memory failed a read/write test – rarely a software issue, often… Moderate P0626 Powertrain The alternator reports a field signal stuck at or near full output – battery, alternator… Moderate P0638 Powertrain The electronic throttle or diesel intake throttle can't reach its commanded angle, often due… Moderate P0670 Powertrain The engine computer can't properly control or hear back from the diesel's glow plug control… Low P0671 Powertrain The glow plug in cylinder 1 or its wire isn't drawing normal current. Usually the plug itself… Low P0690 Powertrain The ECM still sees power coming through its main relay when the relay should be off – often… Low P06DD Powertrain The ECM commanded an oil pressure change and the measured pressure didn't respond – check… High P0742 Powertrain The converter lockup clutch stays applied when it should be released, which can stall… High P0852 Powertrain The park/neutral input reads too high, usually from an open circuit, unplugged connector or bad… Low P1101 Chevrolet · Powertrain GM's engine computer found that measured airflow doesn't agree with what it expects. Low P1129 Jeep · Powertrain The PCM couldn't switch bank 2 of your Jeep's V6 or V8 into oxygen-sensor-controlled fueling… Low