What causes unstable idle speed after engine overheating?

[DelAvery]

Unstable engine idle speed is mainly caused by the following reasons: Intake manifold or various valve leaks When unwanted air, gasoline vapor, or exhaust gases enter the intake manifold, it causes the air-fuel mixture to become too rich or too lean, resulting in abnormal engine combustion. Excessive carbon buildup in throttle body and intake passages Common symptoms include: oil deposits or carbon buildup on the throttle body; oil deposits or carbon buildup in the intake passages around the throttle body; oil deposits or carbon buildup on the idle speed stepper motor, duty cycle solenoid valve, or rotary solenoid valve. Idle air control actuator malfunction Faulty idle air control actuators lead to inaccurate idle air regulation. Common causes include: damaged or stuck throttle motor; damaged or stuck idle speed stepper motor, duty cycle solenoid valve, or rotary solenoid valve. Inaccurate air intake measurement Common symptoms include: malfunctioning air flow meter or its circuitry; faulty intake pressure sensor or its circuitry; poor contact due to water ingress in the engine control unit connector or internal ECU failure.