What Causes Fluctuating Idle Speed During Cold Start?

[LeEmilia]

Here are the specific reasons for fluctuating idle speed during cold start: 1. Intake manifold leakage: When unauthorized air, fuel vapor, or exhaust gases enter the intake manifold, causing the air-fuel mixture to become too rich or too lean, resulting in unstable engine idle. 2. Excessive carbon buildup in throttle body: Carbon deposits in the throttle body and surrounding intake passages alter the air channel cross-sectional area, preventing the control unit from precisely regulating idle air intake. This also leads to improper air-fuel mixture and unstable idle. 3. Faulty intake system components: The engine intake system contains numerous actuators such as throttle motor, idle speed control valve, duty cycle solenoid valve, mass airflow sensor, and intake pressure sensor. Malfunctions in any of these components can cause unstable idle speed.