I have a '90 pickup with the 22re. Just did a full rebuild on it. When I first fire it up it runs great! Until it starts getting warm. About the time the thermostat opens up it starts getting rough and gradually gets worse until it dies. I've been reading thru these forums for weeks now and keep trying different things that I find on here but I'm still not getting this resolved. I've replaced the mass airflow and coolant temperature sensor already. Any guidance on direction would be greatly appreciated.

 

Which coolant temp sensor did you replace? There are 2. One for the gauge and one for the ECU.
I'd also check for vacuum leaks in all the intake piping and hoses and even though its just been rebuilt, do a compression test with the engine warm to see if the heat is opening something up

 

Robert M. I replaced the green one for the ECU. I noticed it revs a little higher when I press the brake in. So I'm wondering if it's a vacuum leak as well. I'm gonna go thru and check them thoroughly. As well as do a compression check tomorrow.