Well, there is an ignition problem that can cause this when the engine gets hot and it stalls. It's caused by a lack of spark which can be either the ECU's fault (on EFI cars), or the coil on pretty much any car. Heat causes expansion. The ECU or the coil gets hot and expands.

What causes a car to not start when it's hot outside?

The most common reason why a hot engine will not start is because the problem is related to fuel. When your new car engine is too hot, fuel cannot circulate well, due to the way vapor obstructs its workings and therefore the engine just will not start, as it should.

What causes an engine to stall at idle?

Stalling problems trace back to three primary causes: a lack of fuel, not receiving enough air, or insufficient power. Common reasons include an empty gas tank, a faulty fuel pump, a bad ignition coil, fouled spark plugs, water in the fuel, or a failing sensor. An engine stall is never fun.