Why does the engine shake when starting?

[LeReed]

If you notice significant body shaking when starting the vehicle or when the vehicle is idling with the engine running, it may indicate one of the following three conditions: 1. Severe engine carbon buildup: The most common cause of car shaking is a dirty throttle body or excessive carbon deposits in the fuel injectors. When there is too much carbon buildup inside the engine, the gasoline sprayed by the cold-start injector can be largely absorbed by the carbon deposits, resulting in an overly lean air-fuel mixture during cold starts. This makes starting difficult. In this situation, the car will only start easily once the carbon deposits have absorbed enough gasoline to become saturated. After starting, the gasoline adsorbed on the carbon deposits will be drawn into the combustion chamber by the engine's vacuum suction, making the air-fuel mixture too rich. This fluctuation between lean and rich mixtures causes idle shaking after a cold start. The lower the temperature, the more fuel is required for a cold start, and the presence of carbon deposits will significantly affect the success of the cold start. 2. Ignition system issues: Check the condition of the spark plugs, high-voltage wires, and ignition coils. Poor performance in the ignition system or weak sparking from the spark plugs can also lead to such symptoms. 3. Unstable fuel pressure: If you have already cleaned the engine carbon deposits, serviced the throttle body, replaced the gaskets and spark plugs, but still notice body shaking at idle, it is recommended to visit a 4S shop to check the fuel supply pressure and the intake pressure sensor. Abnormal fuel pump pressure or incorrect readings and poor performance from the intake pressure sensor can both cause body shaking. 4. Aging engine components: Car shaking can also be related to aging engine mounts (also known as engine mounts). Engine mounts act as the engine's vibration damping system, absorbing minor vibrations during operation. If the engine mounts are faulty, these vibrations will be transmitted to the steering wheel and the cabin, causing shaking at idle.