What Are the Possible Causes of High Idle Speed?
3 Answers
High idle speed is generally caused by excessive carbon buildup in the throttle body or a malfunctioning idle air control valve, which leads to increased air intake. Here is more information about car idle speed: 1. Introduction: Idle speed refers to a state of operation where the engine runs in neutral gear. The engine speed during idle is called the idle speed. The idle speed can be adjusted by modifying the throttle opening size. 2. Diagnosis of Unstable Idle: (1) Fuel system issues: Faulty fuel injectors; Fuel pressure problems; Inaccurate fuel injection volume. (2) Ignition system issues: Ignition module and ignition coil; Spark plugs and high-voltage wires; Inaccurate ignition timing.
My car also had the issue of high idle speed before, hovering around 1100 RPM. There are quite a few common possibilities, such as a dirty throttle body affecting the air intake, carbon deposits making the engine breathe poorly, or an inaccurate air flow meter causing incorrect fuel injection. For the electronic system, a faulty coolant temperature sensor can make the computer misjudge the cold start condition, and a stuck idle control valve can also prevent the RPM from dropping. A vacuum leak is also a critical point—I once encountered an aged and cracked vacuum hose, and the hissing sound of the leak was particularly obvious. The most troublesome issue is with the ECU programming, but this is rare in regular cars. I suggest checking the simplest things first, like the vacuum hoses and sensor connectors, and if that doesn’t work, then scan for trouble codes.
When encountering high idle speed, we usually conduct step-by-step troubleshooting. First, inspect the mechanical components: whether the throttle body has excessive carbon buildup, if the idle air control valve is functioning properly, and if there are any vacuum leaks in the intake manifold seals. Then, check sensor data, such as whether the coolant temperature sensor readings match the actual coolant temperature, and if the air flow meter readings are accurate. For the fuel system, consider whether the fuel injectors are leaking or if the fuel pressure regulator diaphragm is ruptured. If all these are normal, consider abnormal ECU adaptive values or programming errors. In a previous case, the idle speed remained high after the owner cleaned the throttle body without performing a relearn procedure. It's best to use a diagnostic tool to read real-time data streams, which is much more reliable than blindly replacing parts.
