What Causes an Engine to Idle at an Abnormally High Speed?
3 Answers
An engine idling at an abnormally high speed can be attributed to the following reasons: 1. Fuel Injection System: Insufficient fuel system pressure or clogged fuel injectors leading to poor atomization can cause idling issues. Check if the fuel filter is clogged or dirty, and replace it if any abnormalities are found. Inspect whether the fuel pressure regulator is functioning properly, then check the fuel pressure. The normal fuel pressure should be between 250kpa and 300kpa. 2. Idle Control System: A dirty or stuck idle control valve or a broken control circuit can prevent the engine from increasing idle speed as commanded by the computer. If the air intake cannot meet the load requirements, it may result in idling issues or stalling.
I've encountered the issue of high engine idle speed, which is usually caused by extra air leaking into the intake system. Components like vacuum hoses or cracked pipes allow air to sneak in, causing the engine to draw in more fuel mixture and resulting in RPM surges. Another common culprit is a dirty or stuck throttle that fails to close properly, or faulty sensors like the mass airflow sensor misleading the ECU into thinking more power is needed. Prolonged high idle not only wastes fuel but accelerates wear, even affecting emissions. My advice: first inspect engine bay hoses for obvious damage or looseness. If you lack experience, it's best to visit a professional shop for an OBD scan to pinpoint the root cause. Address it promptly to prevent minor issues from turning into costly repairs.
High idle speed is quite common in my many years of driving experience. Most of the time, it's due to excessive carbon buildup in the throttle body causing it to stick, or a faulty sensor like the throttle position sensor failing to send signals. The ECU receives incorrect data and commands higher idle speed. Other cases involve a malfunctioning idle control valve or blockage by dirt. I've found that regular cleaning of the throttle body and sensor connectors can prevent this, but severe cases may require complete replacement. This issue is quite annoying—you'll feel the engine roaring and difficulty controlling acceleration, especially in city traffic where it significantly increases fuel consumption. I recommend not delaying and getting it checked promptly to reduce safety risks.
