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Why does the idle speed not drop when the accelerator is released?

2 Answers

MacCarlos

07/25/25 3:52am

When the car starts and the accelerator is released, the idle speed may temporarily remain high for 1-2 minutes, which is a normal phenomenon. However, if the idle speed fails to drop for an extended period, it may indicate an engine issue. The specific causes are as follows: 1. Throttle valve malfunction. The throttle valve primarily controls the engine's air intake volume. A faulty throttle valve can cause errors in its opening degree, reducing sensitivity and preventing it from closing properly during idle, leading to abnormal idle speed and failure to drop when the accelerator is released. 2. Idle speed control valve malfunction. Located on the throttle body, the idle speed control valve adjusts the idle speed by controlling the air bypassing the throttle body when the throttle is fully closed during idle. A faulty idle speed valve can prevent proper idle speed adjustment, causing unstable idle and failure to drop. 3. Coolant temperature sensor malfunction. The coolant temperature signal is crucial for the engine control unit (ECU) to determine idle speed. A faulty sensor can send abnormal signals, disrupting the ECU's idle control function. If the ECU receives a coolant temperature value lower than the actual temperature, the engine idle speed will remain high, and the idle speed will not drop when the accelerator is released.

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SanLeilani

08/10/25 5:09pm

I found that when the throttle is released and the idle speed doesn't drop, it's usually because the throttle valve is stuck or there's carbon buildup, which obstructs airflow. There could be other issues too, like a dirty idle control valve that can't adjust the speed properly, or a vacuum leak in the engine bay letting extra air in and messing with the normal values. Once, while helping someone check this problem, it turned out to be a poor wiring connection or a blown fuse—just tightening the plug or replacing the fuse fixed it. Letting this go on not only wastes fuel but also risks overheating the engine and wearing out parts, so I recommend cleaning the throttle valve or taking it to a repair shop right away—don't delay. During daily driving, keep an eye on the tachometer; even slight abnormalities should prompt a check to prevent major repairs.

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