What Causes Unstable Engine Idling?
2 Answers
Reasons for unstable car idling: 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, leading to unstable idling. 2. Excessive carbon buildup in the throttle body—carbon deposits on 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 also results in an overly rich or lean mixture, causing unstable idling. 3. Faulty intake system actuators—the engine's intake system has many components, such as the throttle motor, idle speed control motor, duty cycle solenoid valve, mass airflow sensor, and intake pressure sensor. Malfunctions or damage to these parts can cause unstable idling.
I've been driving for almost thirty years, and unstable engine idle is quite common. The main causes include air intake system leaks, such as damaged or loose vacuum hoses, which lead to unstable air flow and fluctuating RPMs. Fuel system issues like clogged fuel injectors or a dirty fuel filter can cause uneven fuel delivery, resulting in engine shaking. Worn-out spark plugs are also a key factor; misfires can make the idle erratic. Carbon buildup on the throttle body or intake manifold can cause stuttering. Once, my car had this issue, and after replacing the spark plugs and cleaning the throttle body, the symptoms disappeared completely. For safety, don’t delay getting it checked. During routine maintenance, have a technician scan for trouble codes with a diagnostic tool—it can save you a lot on fuel costs and hassle.
