91 Buick Century

91 Buick Century (110017 org. Miles)
After driving the car for about 15 -20 mins. If temp. Out side is warm the car will start stalling when you apply the break or slow down. I can usually tell when it is trying to die so if I just press the gas it is fine but when I have to stop it will die. I will put it in Park and it will start right back up no problem but when you pit it into gear it will die. But if you start it and press the gas while switching into drive it will go with a lot of hesitation. But next time you need to stop it will die again, untill cooled off. What could it be?