What Causes Unstable Idle Speed When Starting the Engine?

[Maddox]

Reasons for unstable idle speed when starting the engine: Intake manifold leakage: When unauthorized air, gasoline vapor, or exhaust gases enter the intake manifold, causing the air-fuel mixture to become too rich or too lean, it leads to unstable idle speed in the vehicle. Excessive carbon buildup in the throttle body: Too much carbon deposit in the throttle body and surrounding intake passages changes the cross-sectional area of the air passage, making it impossible for the control unit to precisely regulate the idle air intake. This also results in an overly rich or lean mixture, causing unstable idle speed. Faulty intake system actuators: The engine's intake system has numerous actuators, such as the throttle motor, idle speed control motor, duty cycle solenoid valve, mass air flow sensor, and intake pressure sensor. Malfunction or damage to these components can cause unstable idle speed in the vehicle.