Rough idle
If the engine shakes, stumbles or the RPM hunts at idle, one or more cylinders are not burning fuel evenly, or the idle control is struggling.
AreaEngine
UrgencyModerate
Can I keep driving? Drivable with care. Diagnose soon: performance, economy or other components can be affected.
Common causes
Worn spark plugs or failing ignition coil
A weak spark in one cylinder causes a misfire you can feel.
Vacuum leak
Unmetered air at idle makes the mixture lean.
Dirty throttle body
Carbon around the throttle plate restricts idle air.
Dirty MAF sensor
Incorrect air measurement upsets the mixture.
Clogged fuel injector
One cylinder runs lean.
Worn engine mounts
The engine may run fine but shake the car excessively.
What to check
- Read fault codes: misfire, fuel trim and idle codes point the way.
- Listen for hissing vacuum leaks with the engine running.
- Clean the throttle body and MAF sensor.
- Inspect spark plugs.
Related OBD2 codes
- P0300 Random/Multiple Cylinder Misfire Detected
- P0301 Cylinder 1 Misfire Detected
- P0171 System Too Lean (Bank 1)
- P0505 Idle Air Control System
- P0506 Idle Air Control System RPM Lower Than Expected
- P0507 Idle Air Control System RPM Higher Than Expected
- P0101 Mass or Volume Air Flow Sensor "A" Circuit Range/Performance
Repair guides
Other engine problems
General guidance only. A qualified technician can confirm the cause; brakes, steering and fuel leaks should be checked professionally if in doubt.