What Causes High Idle Speed in Vehicles?

[VanMila]

Vehicle high idle speed causes are as follows: Idle switch not closing: The rotation speed signal determines the fuel injection quantity and timing, but the engine is actually operating under idle conditions with reduced air intake, causing over-rich mixture and increased RPM. Faulty idle air control valve: When idle speed exceeds the set value, the ECU commands the idle control valve to reduce the bypass air intake. Issues like sticky valve movement due to oil contamination/carbon deposits or incomplete throttle closing prevent proper idle adjustment by ECU, resulting in unstable idle. Intake manifold air leakage: The idle control valve opening strictly follows a mathematical relationship with air intake volume. Air leaks disrupt this relationship, making the air flow sensor unable to detect actual intake volume. This leads to inaccurate ECU air intake control and unstable engine idle.