Quick answer
A car that shakes while idling, but smooths out when you accelerate, usually has a problem in the engine's air, fuel, or ignition system — most commonly worn spark plugs, a dirty fuel injector, or a failing ignition coil causing a slight misfire at low rpm.
Common causes
- Worn or fouled spark plugs causing a rough idle misfire
- A dirty or clogged fuel injector delivering uneven fuel spray
- Worn engine mounts letting normal vibration transfer to the body
- A dirty throttle body or faulty idle air control valve disrupting airflow
How to diagnose it
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Note when the shaking happens
If it appears only at idle but clears above 1000 rpm, focus on ignition and fuel. If it worsens in gear, suspect engine or transmission mounts.
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Scan for misfire codes
Use an OBD2 scanner. Even without a check engine light, pending codes like P0300 point to a specific cylinder or random misfire.
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Inspect spark plugs and coils
Check plug gap and condition, and look for cracks in coil boots. Swap coils between cylinders to see if the misfire moves.
When to see a mechanic
- The shaking is accompanied by a check engine light
- You notice a loss of power or stalling
- The vibration is clearly from the drivetrain, not the engine
Related questions
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