What Causes a Car to Stall at Idle Speed?

[ORhett]

There are many reasons why a car may stall at idle speed, such as leaks in the intake system, low fuel pressure, clogged air filters, fuel injector atomization leaks, improper idle adjustment, faulty spark plugs, or malfunctioning air flow meters. Unstable idle speed leading to stalling is one of the more common issues in older cars, with symptoms including fluctuating RPMs and idle speed dropping low enough to cause stalling. The root of the problem can often be traced to aspects related to idle speed control. The car's idle speed is primarily controlled by a small throttle opening or a bypass air passage. When the engine is idling, the throttle is either fully closed or only slightly open. Under stable idle conditions, the engine's idle speed is managed through closed-loop control.