What are the symptoms of unstable car idle speed?

[AlejandroRose]

The symptoms of unstable car idle speed include: 1. The tachometer fluctuates up and down when the engine is idling; 2. The engine shakes. The troubleshooting methods for unstable car idle speed are: 1. Check for air leaks in the intake pipe, PVC valve hose, and oil dipstick; 2. Check if the air filter element is too dirty; 3. Check if the cold start injector and temperature-time control switch are functioning properly. The causes of unstable car idle speed are: 1. Air, gasoline vapor, or exhaust gas entering the intake manifold, causing the mixture to be too rich or too lean; 2. Faulty ignition module, incorrect spark plug gap, spark plug electrode erosion or damage, excessive resistance in high-voltage wires; 3. Clogged fuel injectors, clogged fuel filter, clogged fuel pump screen, faulty fuel pressure regulator, clogged return fuel pipe, etc., leading to a mixture that is too rich or too lean.