Reasons Why the Idle Speed Doesn't Drop Immediately After Releasing the Throttle
2 Answers
When starting the car and releasing the throttle, the engine will idle for a moment, typically lasting 1-2 minutes, which is a normal phenomenon. 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 doesn't drop immediately after releasing the throttle: 1. Throttle Body Malfunction: The throttle body primarily controls the amount of air entering the engine. A faulty throttle body can cause errors in the throttle opening angle, reducing its sensitivity and preventing it from closing properly during idle, leading to abnormal idle speed and the failure of the idle speed to drop after releasing the throttle. 2. Idle Air Control Valve (IACV) Malfunction: The idle air control valve is located on the throttle body. During idle, the throttle is fully closed, and the idle speed is adjusted by controlling the amount of air bypassing the throttle body. A faulty idle air control valve can prevent proper idle speed adjustment, causing unstable idle and preventing the idle speed 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 can 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 won't drop after releasing the throttle.
After years of driving, I've noticed that the idle speed doesn't drop promptly after releasing the accelerator, likely due to engine management issues. When the throttle body is severely carbon-fouled, its movement is hindered, preventing quick closure and return; or the idle control valve may be stuck, causing signal transmission issues that result in falsely high RPM. During maintenance, I regularly check the intake system for leaks, such as cracked or aged intake pipes that allow excess air to enter, making ECU control inaccurate. High idle speed not only wastes fuel and money but also produces thicker exhaust emissions, which are environmentally unfriendly. Whenever I sense abnormalities, I always use an OBD scanner to read fault codes, promptly cleaning the throttle body or replacing parts to prevent minor issues from escalating into major repairs. Safety comes first, especially when unstable idle speed in parking lots or at traffic lights can easily lead to loss of control, which is frightening—prompt professional inspection is crucial.
