What Causes Occasional High Idle Speed?
1 Answers
The reasons for occasional high idle speed are as follows: Idle switch not closing: The rotation speed signal determines the fuel injection volume and injection time. However, when the engine is operating under idle conditions, the reduced air intake leads to an overly rich air-fuel mixture, causing the speed to rise. Faulty idle control valve: When the idle speed exceeds the set value, the ECU commands the idle control valve to reduce the intake bypass passage, decreasing the air intake and lowering the engine speed. Issues such as sticky movement of the idle control valve due to oil contamination or carbon deposits, or incomplete closing of the throttle valve, prevent the ECU from correctly adjusting the engine idle speed, resulting in unstable idle conditions. Intake manifold air leakage: The opening degree of the idle control valve and the air intake strictly follow a certain functional relationship—where an increase in the valve opening corresponds to an increase in air intake. Air leakage in the intake manifold disrupts this strict functional relationship between the air intake and the idle control valve opening. As a result, the air flow sensor cannot accurately measure the actual air intake, leading to inaccurate air intake control by the ECU and causing unstable engine idle speed.
