What Causes the Engine to Shake Every Few Seconds at Idle Speed?

[VanElisa]

Engine shaking every few seconds at idle speed can be caused by the following reasons: Misfire: Check the condition of the spark plugs, high-voltage wires, and ignition coils. Poor performance of the ignition system or weak spark plug firing can lead to this issue. Severe carbon buildup: The most common cause of engine shaking is excessive carbon deposits on the throttle body or fuel injectors. When there is too much carbon buildup inside the engine, the gasoline sprayed by the cold-start injector is largely absorbed by the carbon deposits, resulting in an overly lean air-fuel mixture during cold starts. Only when the carbon deposits become saturated with gasoline can the engine start easily. After starting, the gasoline adsorbed on the carbon deposits is drawn into the combustion chamber by the engine's vacuum, making the air-fuel mixture too rich.