Car Shakes at Idle — Engine, Mount, or Misfire?

What's happening

The engine is supposed to idle smoothly because each cylinder fires evenly. Shaking at idle means one or more cylinders is contributing less power than the others. Or the engine is running fine but the broken motor mount is letting normal vibration transmit to the chassis. Test: in Neutral or Park, does the shaking improve? If yes, the engine is fine but the mount is bad. If no change, you have an actual misfire or vacuum leak.

You might also notice

• Vibration in the steering wheel and seat at stops
• May smooth out at higher RPM
• Sometimes the gear selector shakes visibly
• Possibly a check engine light

Likely causes (most common first)

1. Misfire on one or more cylinders (worn plug, failing coil)
2. Vacuum leak
3. Failed motor or transmission mount (the engine moves more than it should)
4. Idle air control problem
5. Carbon buildup on direct-injection valves

What to check first

1. In Neutral or Park, does the shaking get better? Mount issue if so
2. Read codes — misfires are obvious
3. Visually inspect the motor mounts (engine sags more on one side, rubber mount cracked)

Common OBD2 codes for this symptom

Don't have the code yet? Look up your code or read it with AXLY.pro.

Can I keep driving?

Yes. Diagnose within a few weeks — broken mounts and misfires both progress.

Confirm with the actual code

Symptom-based diagnosis narrows the field — reading the actual stored code finishes the job. AXLY.pro is a free iPhone app that pairs with any Bluetooth OBD2 adapter and reads every stored DTC.