What Causes Unstable Idle and Shaking After Car Startup?

[Kingston]

There are several reasons for engine shaking and unstable idle, including excessive engine carbon buildup, increased spark plug gap, and abnormal coolant temperature. Below are detailed explanations of these causes: Excessive Engine Carbon Buildup: When there is too much carbon buildup inside the engine, the gasoline sprayed by the fuel injector during startup is largely absorbed by the carbon deposits. This results in an overly lean air-fuel mixture, making it difficult to start the vehicle. Only when the carbon deposits become saturated with gasoline does the vehicle start more easily. Increased Spark Plug Gap: During a cold start, the engine temperature is insufficient, and the fuel injector sprays more gasoline to meet power demands. The fuel requires higher ignition energy, but an increased spark plug gap reduces ignition energy, subsequently affecting performance and causing the vehicle to shake.