Symptom guide
Rough Idle
How to diagnose shaking, uneven RPM, or stumbling when the car is stopped.
Quick answer
Rough idle can come from misfires, vacuum leaks, dirty air metering, fuel issues, or engine mounts.
Most likely causes
- Ignition misfire
- Vacuum leak
- Dirty throttle body
- MAF sensor fault
- Worn engine mount
Basic driver checks
- Watch RPM movement.
- Check for flashing check engine light.
- Scan for misfire and lean codes.
- Listen for hissing or ticking.
DIY diagnostic path
- Inspect plug and coil history.
- Check intake hoses.
- Review freeze-frame data.
- Stop driving if the light flashes.
Common mistakes
- Ignoring a flashing light
- Replacing mounts before checking misfires
- Cleaning sensors with the wrong spray
What to tell the mechanic
Say whether the idle is rough only cold, only warm, in gear, or with AC on.