1995 Chevy Corsica Corsica wont run when warmed up

I have a 1995 corsica that runs great when cold. After it warms up and I shut off it will not start back untill it cools off. I appear to have both spark and fuel. Just will not start. I have also noticed that if I get on freeway that the ck engine light comes on. Does not do that if I drive on roads off the freeway. Dont know if connected ot not. Have changed both spark plug wires as well as fuel pump.