Rough Idle: Why Your Engine Shakes at a Stop

When your vehicle shakes or shudders while stopped at a light, the engine is running unevenly—usually because one or more cylinders aren't firing the way they should.

Common culprits include worn spark plugs, failing ignition coils, clogged fuel injectors, vacuum leaks, or a dirty throttle body.

A rough idle rarely fixes itself. Left alone, it can damage the catalytic converter and reduce fuel economy.