What are the causes of fluctuating car idle speed?
1 Answers
Car idle speed fluctuations can be caused by intake manifold or various valve leaks, excessive carbon buildup in the throttle body and intake passages, faulty idle air control components, or incorrect signals received by the air intake control unit. Intake manifold or various valve leaks: When unwanted air, fuel vapor, or exhaust gases enter the intake manifold, it leads to either too rich or too lean air-fuel mixture, causing abnormal engine combustion. Excessive carbon buildup in throttle body and intake passages: When there's too much carbon deposit or dirt in the throttle body and surrounding intake passages, the air channel cross-sectional area changes. This prevents the control unit from precisely regulating idle air intake, resulting in improper air-fuel mixture and abnormal combustion. Faulty idle air control components: Malfunctioning idle air control components lead to inaccurate idle air control. Incorrect signals received by air intake control unit: When the air intake control unit receives wrong signals and issues incorrect commands, it causes inaccurate idle air intake control, leading to abnormal engine combustion. This is an indirect cause of unstable idle speed. Solutions for fluctuating car idle speed: When experiencing unstable idle speed, first adjust the idle speed. If the problem persists after adjustment, check whether the idle jet and idle air jet are clogged. If clogged, clean them with gasoline or acetone and blow through with compressed air. If not clogged, stabilize the engine at a certain RPM and listen for air leaks at the intake manifold or carburetor middle/lower gasket areas. If leaks are found, tighten screws or adjust gaskets to resolve. If idle instability is accompanied by reduced engine power, further inspect spark plug conditions, valve sealing performance, and ignition timing. Perform repairs or adjustments if necessary.
