What Causes Engine Stalling at Idle?

[LouisMarie]

Engine stalling at idle can be caused by motor failure, throttle body malfunction, poor fuel quality, etc. The specific reasons are as follows: Motor Failure: Engine idle motor may have sticking issues, the outer insulation of the motor wiring may be worn, or the idle air passage may be too dirty. Timely inspection and motor replacement are required. Throttle Body Malfunction: Problems with the engine throttle position sensor, camshaft position sensor, crankshaft position sensor, or engine speed sensor, or these sensors being too dirty. Poor Fuel Quality: If the gasoline quality is poor, it can also cause such idle issues, requiring the use of higher-quality fuel.

[Wayne]

Having driven for over twenty years, I've found that stalling at idle is most commonly caused by a dirty throttle body. Impurities in gasoline can lead to carbon buildup on the throttle over time, restricting airflow and making the engine prone to stalling at idle. Another common culprit is worn spark plugs, where insufficient ignition energy causes unstable engine operation. Once my car suddenly stalled at a red light, and upon inspection, it turned out to be slightly clogged fuel injectors disrupting proper fuel delivery. Vacuum leaks are also frequent offenders, especially in older vehicles where rubber hoses tend to crack, throwing off intake pressure and causing the engine to stall. Insufficient fuel pump pressure can produce similar symptoms, particularly in summer when high fuel temperatures exacerbate the issue. Idle stalling should never be ignored—prompt diagnosis and repair are essential.

[LeCharlotte]

This issue depends on the specific symptoms. If the engine stalls during cold starts, it's likely due to carbon buildup jamming the idle control valve. If it stalls at red lights when warmed up, it could be aging ignition coils, spark plug wires, or irregular spark plug firing. Stalling with AC on often points to insufficient alternator output or an aging battery. I once encountered stalling when headlights were turned on - turned out to be oxidized battery terminal connections. Modern vehicles with electronic control systems may also stall if the throttle position sensor fails and sends false signals. Watch for abnormal tachometer needle fluctuations at idle - if present, promptly check the oxygen sensor and mass airflow sensor.

[LaLayla]

There are quite a few reasons for idle stalling, the most common being carbon buildup in the throttle body. Especially in stop-and-go city driving, carbon deposits can become particularly severe. Another reason could be a fuel filter that hasn't been replaced for too long, leading to unstable fuel supply pressure and causing the engine to stall. I once drove a used car where a vacuum hose leak caused unstable idle, eventually leading to stalling. Spark plugs overdue for replacement are also a common cause, as excessive gap can affect combustion. Occasionally, a clogged fuel injector might cause a cylinder to misfire. If the engine mount rubber is aged or broken, excessive vibration could also lead to stalling.