Funny you should revive this thread. I actually managed to fix the problem. What it ended up being were the injectors. I had a donor supra, so I swapped out the injectors and voila, problem was solved. My theory was that they were injectors for a turbo model in my NA model. I don't know if this will help you, but I would definitely check to see if the electrical resistance on your injectors are consistent for your model.

God. Bless. YOU! but only if it works for me. :)
 

Thanks a lot gettarobo!! if that turns out to be the solution, i will come and find you wherever you are, i will anoint your head with oil and wash your feet with my hair. LOL

Possible Solution
 

I have a 1989 turbo with recent mild modifications, a slow work in progress. The car backfired badly a few weeks ago at speed, the check engine light came on and I had similar symptoms, would not rev above 4,000 rpms. Checked everything, changed TPS, etc., no luck. Finally found a simple cost free problem. The lower intercooler hose had come off, huge vacuum or pressure leak. Re-attached it and made sure it was secure, problem solved. One possibility. Hope this helps.