What Causes High Engine Idle Speed?
2 Answers
High idle speed is mainly caused by the following reasons: 1. The idle switch fails to close; 2. Malfunction of the idle control valve; 3. Air intake pipe leakage; 4. Incorrect valve timing; 5. Fuel injector dripping or clogging; 6. Exhaust system blockage; 7. EGR valve opening during idle operation. Below are the solutions for high idle speed: 1. Adjust or replace the throttle position sensor; 2. Clean or replace the idle control valve and perform basic idle speed setting with a dedicated decoder; 3. Locate the leakage point and reseal or replace related components; 4. Check timing marks and readjust valve timing according to standards; 5. Clean and inspect each fuel injector's spray volume to ensure no clogging or dripping; 6. Replace the three-way catalytic converter; 7. Remove carbon deposits from the EGR valve or replace the EGR valve.
As someone who has been in the car repair business for many years, I've found that high idle speed is most commonly caused by excessive carbon buildup in the throttle body blocking airflow. When air intake is restricted, the engine control unit misjudges and supplies more fuel, causing the RPM to rise. Other possibilities include aging vacuum hoses with air leaks or a faulty idle control valve sensor. A problematic coolant temperature sensor might also make the system think it's in cold-start mode, maintaining high idle. When dealing with such issues, I usually advise car owners to first check vacuum hose integrity and try cleaning the throttle body. If that doesn't work, diagnostic tools are needed to read error codes and identify sensor or wiring problems. High idle not only wastes fuel and accelerates component wear but may even cause loss of control while driving in severe cases. I recommend seeking professional repair as soon as possible - don't let minor issues become major problems. Typically, a few hundred dollars for cleaning or part replacement will solve it.
