What causes unstable engine idle speed in a car?
2 Answers
Unstable engine idle speed in a car may be caused by throttle valve issues or excessively dirty intake passages, among other factors. Such situations require professional inspection and repair at a 4S shop. The following are the impacts of unstable engine idle speed: 1. Comfort: The vibration caused by unstable engine idle speed will reduce vehicle comfort. 2. Fuel economy: Due to uneven operation of the cylinders, the engine control unit will frequently adjust the engine's operating conditions, causing the engine to operate in an open-loop state, which will lead to decreased fuel economy. 3. Component lifespan: Because the engine will vibrate at idle, the engine and transmission fixing pawls will work frequently, thereby shortening their lifespan.
I've been driving this car for ten years, and it occasionally has unstable idling. When the car stops, the engine shakes erratically, and the tachometer fluctuates up and down, which is really annoying. Carbon buildup is the most common issue; long-term low-speed driving leads to carbon accumulation clogging the intake ports, causing uneven combustion due to poor airflow. Worn-out spark plugs are another major cause, as incorrect ignition timing makes the engine shake. Leaks in the vacuum lines can allow extra air to sneak in, disrupting the air-fuel ratio control. When idling is unstable, the car struggles to start and may even stall, affecting daily commutes. I suggest running the engine at high speed on the highway for half an hour every six months to clear carbon buildup and regularly replacing spark plugs as a preventive measure. If the problem persists, don't delay—take it to a repair shop for a computer diagnostic to check for trouble codes. A small fix now can save you from bigger troubles later.
