What are the reasons for unstable idling speed in a Corolla?

[SanDavid]

The reasons for unstable idling speed in a Corolla are as follows: Excessive carbon deposits or aging of the engine: 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, making it difficult to start. After the car is started, the gasoline adsorbed on the carbon deposits is then sucked into the combustion chamber by the engine's vacuum, making the air-fuel mixture too rich. This fluctuation between lean and rich air-fuel mixtures causes the engine to shake during idling after a cold start. Aging engine mounts: Engine mounts are essentially the shock absorption system of the engine. They are responsible for absorbing minor vibrations when the engine is running. If the engine mounts are faulty, these vibrations can be transmitted to the steering wheel and the interior of the car, causing shaking during idling.