I have a 1986 944 with a 2.5. I can put in a new set of plugs and drive 30 miles shut it off and then it's real hard to start. Pull the plugs and there real black. What would cause it to run rich. I pulled a compression test and all 4 are around 125 with the throttle closed.

 

Plenty of things. Let's start easy - when's the last time you changed the O2 sensor? After that, you might want to test your AFM for dead spots.

 

FPR. When it fails your fuel pressure will run way high and you will run rich. It will also leak down fuel pressure when you stop causing hot start problems. Is your fuel pump loader than you think it should be (another symptom).

I'd measure fuel pressure and leak down to be sure before I spent the dough o the part.