Fionnla

My friend's 88 Stock Trans AM 305 TBI has a stalling problem after warmed up. You can drive it around for a while and then shut it off for maybe an hour and then start it back up and drive for a block or two and it stalls and does not want to start. He was told to take off the gas cap and relieve the pressure and then try to start it and it started right up and ran good. It's done that about 3 or 4 times now, and each time , he took the gas cap off and put it back on and it ran good to the house, at one time he was 15 miles away. Each time it was when he let it set for a while after being warmed up good. No check-engine light comes on. His mechanic could not find anything wrong. Maybe someone can help with this problem. The car runs great except for that problem.
Thank You.