What is the reason why the idle speed of cars is sometimes high?

The following is a detailed explanation of the reasons for the high idle speed of the car and the solution: 1, the throttle is stuck and closed: pull the throttle rocker in the closing direction, and the idle speed of the engine can be reduced to normal speed, and then the throttle is stuck and closed. Solution: Replace the cable, remove and clean the throttle body. 2, additional air valve failure. Solution: Replace the additional air valve. 3. Idle speed control valve failure: check the action sound of idle speed control valve. If there is no action sound, the control valve is faulty. Solution: Replace the control valve. 4. The water temperature sensor is faulty. Solution: Input too low water temperature signal to the computer. 5, air conditioning switch, power steering gear pressure switch failure. 6, crankcase forced ventilation valve failure. Solution: Positive crankcase ventilation valve. 7. Air leakage in the air intake system. Solution: Find the leakage point, reseal or replace the relevant parts. 8. The charging voltage of the generator is too low. Solution: overhaul the engine.