What Are the Causes of High Car Idle Speed?
2 Answers
The causes of high car idle speed are as follows: First, the idle speed control valve malfunctions. Normally, electronic fuel injection engines determine the normal idle speed through the idle speed control valve. During driving, the electronic control unit calculates based on the information transmitted by the car engine to adjust the intake air volume, thereby changing the engine's idle speed. However, if oil stains or carbon deposits affect the idle speed control valve, the electronic control unit cannot receive accurate information, which in turn affects the adjustment of the idle speed, leading to excessively high idle speed. Second, there is a leak in the intake system. Maintaining normal idle speed requires strict control of the intake air volume. When the intake system leaks, the electronic control unit cannot perform accurate calculations, resulting in an increased intake air volume and consequently excessively high idle speed. Third, the fuel injector leaks or is clogged. When the fuel injector leaks or is clogged, it causes issues in the car's internal fuel injection system, leading to either excessively high or low concentration of the internal mixture. This inevitably affects the cylinder's operation, causing unstable idle speed.
From my perspective, high idle speed issues are quite common, mostly related to the engine's intake or control system. Excessive carbon buildup in the throttle body can obstruct smooth air intake, prompting the ECU to automatically raise RPMs as compensation; similarly, a stuck or dirty idle control valve (which regulates airflow) can cause erratic idling when malfunctioning. Vacuum leaks are a major culprit – cracked or loose intake manifold joints allow unmetered air to enter, tricking the ECU. Sensor failures (like faulty oxygen or temperature sensors) often mislead the ECU into maintaining high idle, while leaking fuel injectors or unstable fuel pressure also increase RPMs. For DIY troubleshooting: start by cleaning the throttle body and listening for vacuum hose hisses; if unresolved, visit a professional shop for diagnostic scanning – prolonged high idle wastes fuel and risks engine damage.
