1990 Chevrolet Astro, 4.3L TBI, runs smooth until it heats up, then acts as if it has a miss, and runs rough. It appears one of the throttle body injectors is not spraying fuel when it's running rough. I replaced both the TBI injectors, and the ignition coil, and still no change in how it runs. Any ideas would be appreciated.

When it idles rough it could be several things but, an easier thing you can do 1st is cleat the throttle body of any carbon(black stuff) with throttle body cleaner or something like carb cleaner. Ive used brake cleaner sometimes. But yea, look up your cars info about your motor and just clean all the black carbon off of anything at the throttle body and you may even need to take some of it apart to get down in there with a rag, little cleaning brush and the cleaner. Clean the thing you can move by hand called a "butterfly".

a bad distributor is the most common problem of stalling,rough idle and backfiring.

With that kind of symptoms you should be displaying a check engine light have the codes extracted and get back to me let me know what codes and I will give you a better idea of what is wrong with your vehicle.

sounds real easy either a bad idle air control solenoid or more likley a blown throttle body gasket. to test fro a blown gasket, with engine running and cool spray carb cleaner or brake cleaner around base of tb were it bolts to intake. when it hits the bad area, should idle down and be normal for a second or 2. iac is possible,try this first since its so common and let me know

Sounds like the engine has a vacuum leak at the throttle body area.

check fuel pressure

have mass airflow sensor cked.

fuel pressure isnt right.. need to get a fuel pressure regulator so you can regulate the gas flow..

I had the same problem with my van and ended up being the TBI base gasket

timing? if you've got gas and you've got spark, have you checked the crank/cam shaft position sensors? have you put a timing light on it to see if you might have jumpped timing?