What is Idle Speed?

[Gretchen]

Idle speed refers to an operating condition of a car where the engine runs in neutral gear. Below are the reasons for its occurrence: Various Valve Leaks: When air, gasoline vapor, or combustion exhaust that should not enter the intake manifold does so, it causes the air-fuel mixture to become too rich or too lean, leading to abnormal engine combustion. If the leak affects only individual cylinders, the engine may experience severe shaking, particularly impacting cold idle conditions. Common causes include: loose intake manifold clamps or cracked rubber hoses; intake manifold gasket leaks; damaged intake manifolds or other components causing holes in the intake manifold; leaking O-ring seals on fuel injectors; disconnected or broken vacuum tube connectors; excessive opening of the Positive Crankcase Ventilation (PCV) valve; a constantly open charcoal canister valve; or an Exhaust Gas Recirculation (EGR) valve that does not close properly. Excessive Carbon Buildup in the Throttle Body and Intake Tract: Excessive carbon deposits and dirt in the throttle body and surrounding intake tracts alter the cross-sectional area of the air passage, making it difficult for the control unit to precisely regulate idle air intake. This results in an overly rich or lean air-fuel mixture and abnormal combustion. Common causes include: oil or carbon buildup in the throttle body; oil or carbon deposits in the intake tracts around the throttle body; or oil and carbon buildup in the idle speed stepper motor, duty cycle solenoid valve, or rotary solenoid valve. Idle Air Actuator Malfunction: Faulty idle air actuators lead to inaccurate idle air control. Common causes include: damaged or stuck throttle motor; or damaged or stuck idle speed stepper motor, duty cycle solenoid valve, or rotary solenoid valve.