What are the causes of unstable idle speed?
1 Answers
Reasons for unstable idle speed in cars: 1. 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, leading to unstable idle speed. 2. 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 idle air intake. This also results in an overly rich or lean mixture, causing unstable idle speed. 3. Faulty intake system components: There are many actuators in the engine's intake system, such as throttle motor, idle speed control stepper motor, duty cycle solenoid valve, air flow meter, intake pressure sensor, etc. Malfunctions or damage to these components can cause unstable idle speed. 4. Fuel system faults: Issues like clogged fuel injectors, blocked fuel filter, obstructed fuel pump screen, faulty fuel pressure regulator, or blocked return line can all lead to incorrect fuel injection, causing the mixture to be too rich or too lean, resulting in unstable idle speed. 5. Ignition system faults: Problems such as faulty ignition module, incorrect spark plug gap, eroded or damaged spark plug electrodes, or excessive resistance in high-voltage wires can reduce ignition spark energy or cause misfires, leading to erratic idle speed fluctuations.
