Reasons for High Idle Speed When Releasing the Throttle

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When starting the car and releasing the throttle, a high idle speed may occur momentarily, lasting for about 1-2 minutes, which is normal. However, if the idle speed remains high for an extended period, it may indicate an engine issue. Below are the specific reasons why the idle speed does not drop when releasing the throttle: 1. Throttle valve malfunction: The throttle valve primarily controls the amount of air entering the engine. A faulty throttle valve can cause errors in its opening degree, reducing its sensitivity and preventing it from closing properly during idle, leading to abnormal idle speed and the phenomenon of high idle speed when releasing the throttle. 2. Idle control valve malfunction: The idle control valve is located on the throttle body. During idle, the throttle valve is fully closed, and the idle speed is adjusted by controlling the amount of air bypassing the throttle body. If the idle control valve is faulty, it will prevent the idle speed from being adjusted correctly, causing unstable idle speed and preventing it from dropping. 3. Coolant temperature sensor malfunction: The coolant temperature sensor signal is crucial for the engine control unit (ECU) to determine the idle speed. A faulty coolant temperature sensor will send abnormal signals, disrupting the ECU's idle control function. If the ECU receives a coolant temperature value lower than the actual value, the engine idle speed will remain high, and the idle speed will not drop when releasing the throttle.