In an 87 SE 2.8, 24k miles..... The car starts and runs perfectly in most every situation. I can drive it as long as I want with no issues, however...... Shutting down the car and letting it heal soak and a subsequent start up, it runs rough until the temps stabilize. Then it cleans out and runs perfect again. Typical when I stop for gas. in that short time of a fill up, after start ip it runs rough for 20-30 seconds and then clears up. It seems like the longer I let it heat soak, the longer it runs crappy after the start up unless I let it cool down some. then it works perfect. The only time it acts up when running is when stuck in traffic in the hot summer with the a/c on and the temps getting high. Traffic starts moving, airflow picks up and again once temps drop it runs perfect. My best guess would be the coolant temp sensor located up by the fill neck. Any other thoughts?
Leaking fuel injector. Dribbles fuel into the intake manifold. Makes it start hard when you go to restart it after a short turn off. Fuel pressure remains in the fuel rail as it is supposed to. But fuel should not leak past the injector.
Leave it shut off long enough and the fuel evaporates. But try to restart it when it has only been off for a short time and the fuel is still there.
How to see if this is what is indeed happening? - Start it up and run it a bit. Turn it off and look down the throttle body. There shouldn't be any fuel dribbling down the throttle body throat.
Might just be vapor lock, fuel getting too hot in the lines. Try insulating the lines where they get closest to the manifold. Today's fuel boils at a lower temperature due to the 10% that's not gasoline.