What Causes Unstable Engine Idling?

[VanJackson]

Here are the reasons for unstable engine idling: 1. Excessive carbon buildup in the throttle body and mass air flow sensor. The throttle body and mass air flow sensor are prone to dirt accumulation. Most modern vehicles use electronic throttle bodies, where even minor carbon deposits can affect performance. Excessive carbon buildup in the throttle body may cause throttle hesitation, severe power loss, and unstable idling. 2. Excessive carbon deposits in the cylinder combustion chamber and on pistons. Too much carbon buildup in the combustion chamber can absorb some fuel, slightly prolonging the ignition startup time. Additionally, heavy carbon deposits often form on valves and piston rings, indirectly causing insufficient cylinder compression. 3. Weak spark caused by faulty spark plugs. Spark plugs can also accumulate carbon deposits, which can be cleaned to restore their activity. However, some spark plugs may be nearing the end of their service life, leading to performance degradation. 4. Fuel pressure malfunction. Low fuel pressure results in poor fuel atomization from the injectors, with fuel spraying in lines or even droplets in severe cases, reducing fuel injection quantity and making the air-fuel mixture too lean. 5. Various component failures. Issues such as intake manifold leaks, valve leaks, fuel pressure malfunctions (especially low pressure), and ignition system failures can also cause unstable engine idling.