What is unstable idle speed?

1 Answers
Grayson
07/30/25 8:39am
Unstable idle speed refers to the phenomenon where the engine's tachometer fluctuates up and down while idling, accompanied by engine shaking. The causes of unstable idle speed and shaking in a car include: 1. Severe carbon buildup in the engine. 2. Dirty throttle body or carbon deposits in the fuel injectors. 3. Faulty spark plugs, high-voltage wires, or ignition coils leading to poor ignition system performance. 4. Unstable fuel pressure, insufficient fuel supply from the fuel pump, or incorrect readings from the intake pressure sensor. 5. Clogged fuel lines causing insufficient fuel supply. 6. Aging engine components. Solutions to unstable idle speed and shaking: 1. Clean carbon deposits from the engine and idle speed control valve. 2. Clean the fuel system. 3. Replace spark plugs, high-voltage wires, and ignition coils. 4. Clean the air filter and throttle body. 5. Replace aging engine components.
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