Car starts & runs fine until I drive it a while

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Car starts & runs fine until I drive it about 10 miles and turn it off for 20-30 minutes. When I try to start it back it takes several times to get it to start. I have replaced the throttle positioning sensor, map sensor, fuel filter, spark plugs & wires, and fuel injector trying to fix the problem with no success. (It is actually a 1988 Chevrolet Celebrity NOT a 1990)