1995 Ford Explorer Trouble starting engine when hot

Having a problem on warm days or when car engine is already hot. If I am driving for awhile and then I stop somewhere for a short time and go to start the engine again, it does not want to start, I have to keep my foot on the gas or the car will stall. Sometimes I have to let it run for 20 min. To 40 min. In idle and the one time this happened you can hear the engine wanting to stall and then all of a sudden the engine kicks in and the engine is back to normal and then I could drive away. The last time this happened though I had it running for an hour and it never got better. Then I left the engine off for an hour and then when I went to start it it started ok and I was able to drive away. Do you know what could be the problem with my engine?