What Causes Unstable Idle Speed When Starting the Car in the Morning?

[McEva]

Unstable idle speed when starting the car in the morning can be caused by the following reasons: Intake Manifold Leak: When unauthorized air, gasoline vapor, or combustion exhaust enters the intake manifold, it can cause the air-fuel mixture to become too rich or too lean, leading to unstable idle speed. Excessive Carbon Buildup in the Throttle Body: Too much carbon buildup in the throttle body and surrounding intake passages changes the cross-sectional area of the air channel, preventing the control unit from precisely regulating 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 many actuators, such as the throttle motor, idle speed control motor, duty cycle solenoid valve, mass airflow sensor, and intake pressure sensor. Malfunctions or damage to these components can lead to unstable idle speed.