Vacuum leaks are the most common culprit of a car stalling. An engine requires a pressurized air system to function properly. If too little or too much air enters into the system, the engine will face different intermediate idling issues.
Intermediate stalling occurs when an engine does not receive enough air into the system. There are several vacuum lines that snake around the entirety of the engine. The smallest leak can cause the idle to drop and stall the engine.
An idle air control valve may also be clogged. The idle air control valve controls the idle speed of an engine. The valve can be loosen or tighten to either allow more or less air into the system thereby adjusting the idle. When clogged, the system creates a vacuum leak that causes the engine to stall.