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

P1602 Volkswagen · Powertrain The engine computer saw its constant battery feed drop too low – usually a disconnected, flat… Low P1603 Toyota · Powertrain Toyota's ECM logged that the engine stopped by itself while running, without the key being… Moderate P1605 Toyota · Powertrain On newer Toyotas the idle sagged below about 400 rpm; on some older ones it flags the ECM's… Low P1633 Ford · Powertrain Ford's PCM lost its constant battery feed, so the memory holding learned fuel, idle and shift… Low P2004 Powertrain The intake runner or tumble flaps stay open when told to close, usually a vacuum or linkage… Low P2009 Powertrain The runner or tumble flap solenoid circuit reads too low: a short to ground, an open coil… Low P2015 Powertrain The sensor on the intake manifold flaps reports a position that doesn't match what the ECU… Low P2096 Powertrain The sensor behind the catalytic converter keeps reporting lean, and the ECU has run out of room… Low 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 P2109 Powertrain The closed-throttle reading no longer matches what the computer learned – usually carbon… Low 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 P2176 Powertrain The PCM hasn't stored where the closed throttle sits, usually after a battery disconnect… Low P2187 Powertrain Bank 1 runs lean at idle but recovers once rpm rises, the classic fingerprint of unmetered air. Low P2188 Powertrain At idle, bank 1 gets extra fuel from somewhere the PCM doesn't control; above idle the mixture… Moderate P2196 Powertrain The front sensor on bank 1 keeps claiming rich, so the PCM strips out fuel the engine actually… Low 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 P2237 Powertrain The wire that carries the pump current of the upstream wideband (air-fuel) sensor is open. Low P2238 Powertrain The pump-current wire of the upstream air-fuel sensor is being pulled low, usually by a short… Low P2243 Powertrain The ECM lost the reference-cell signal of the upstream wideband sensor, as if the wire were… Low P2279 Powertrain Air is getting into the engine after the mass airflow sensor, so the computer isn't measuring… Low 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