What is Unstable Idle Speed?

[DiWalker]

Unstable idle speed refers to the fluctuation of the tachometer when the engine is idling, accompanied by noticeable engine vibration. 1. Causes of unstable idle speed: (1) Improper air-fuel mixture ratio in the engine compartment; (2) Prolonged use of spark plugs leading to aging of the ignition coils, high-voltage wires, and potential leakage issues, which reduce ignition efficiency; (3) Carbon buildup on the engine valves and intake passages, which absorbs fuel and reduces the amount of fuel-air mixture available for combustion, thereby decreasing engine power; (4) Malfunctioning coolant temperature sensor. 2. Solutions for unstable idle speed: (1) Replace spark plugs; (2) Clean the valves and intake passages; (3) Inspect the coolant temperature sensor.