Why does the car shake at idle?

[HannahAnn]

Here are the reasons why the car shakes at idle: 1. The temperature inside the engine is insufficient, and the temperatures of both fuel and lubricating oil are low. When the water temperature is low, it is considered a cold start. The engine noise is loud, especially in winter, sounding like a tractor, and the vibration is significant. This condition improves when the engine warms up, which is a normal phenomenon. This is because combustion and lubrication are poor during cold starts, the idle speed is higher when cold, and lower when warm. Poor combustion can easily lead to carbon buildup, causing the exhaust pipe to turn black. Some cars may emit blue smoke for the first few seconds, which is a sign of oil burning and is considered normal. 2. Uneven cylinder pressure or excessive carbon buildup on the intake valves and intake manifold. 3. Poor fuel injection due to excessive carbon deposits inside the fuel injector.