1999 Volkswagen Jetta Car stopes in stoping sighns

I have a 1999 VW jeta, in the hot summer days it stop running when I am at a stop sigh/red light. I start it, and start normally. If parking in a sunny area, in takes longer to start. Checked the fuel pump and the pressure was normal, changed the engine coil, changing oil filter and oil every 2,500-3,000 miles. I was told that the temperature sensor might be another issue, but not sure which issue is the main problem. If on highway with a high speed as I come off the highway and slowing down the car will act like it will cut off and if I stop, the engine will stop. What can I do to prevent that and would it eventually affect the engine or it is only a heating problem? I live in Chicago suburb in IL.

Thanks
Nancy