There are several reasons a warm car may stall, including vapor lock, an overheating fuel pump and ignition coils that are cutting out. Overheating ignition coils may also cause a car to stall when warm.
Vapor lock occurs when the fuel pump does not deliver enough pressure, and the fuel begins to boil in the fuel lines. When this occurs, the fuel begins to vaporize, and no matter what type of engine the car has, it cannot run on only vapors.
If the engine of the car is fuel injected, it may stall when warm due to it not receiving power from the electric fuel pumps. If the fuel pump does not get power, it cannot move the fuel through the system. This can occur in either the fuel pump relay or the automatic shutdown relay, so drivers should check both parts.
Overheating engine coils cutting out may also cause a car to stall when warm. To test this, the driver should check to see if there is a spark in the engine by cranking it. If it is working, a spark and sound occurs. If the car passes this test, the stalling may be caused by an overheating ignition switch. If the key or ignition lock are hot after attempting to start the car, this is likely the cause.