What Causes Difficulty Starting Due to Low Idle Speed?

[GeorgeMarie]

The reasons for difficulty starting due to low idle speed are as follows: Intake Manifold or Various Valve Leaks: When air, gasoline vapor, or combustion exhaust that should not enter the intake manifold infiltrates, it causes the air-fuel mixture to become too rich or too lean, leading to abnormal engine combustion. If the leak affects only certain cylinders, the engine may experience severe shaking, particularly impacting cold-start idle conditions. Excessive Carbon Buildup in Throttle Body and Intake Passage: Excessive carbon deposits and dirt in the throttle body and surrounding intake passages alter the cross-sectional area of the air passage, preventing the control unit from precisely regulating idle air intake. This results in an overly rich or lean mixture and abnormal combustion. Common causes include: oil contamination or carbon buildup on the throttle body; oil or carbon deposits in the intake passages around the throttle body; and oil or carbon buildup on the idle speed stepper motor, duty cycle solenoid valve, or rotary solenoid valve.