Hello TGO, I have been searching for two weeks for a solution to my problem. I have been unsuccessful in getting my motor back to running like a champ.

I have a 1990 Pontiac Firebird Trans Am GTA 305 TPI T5

The problem: The car rpms bounce up and down trying to get past 1100rpm in first gear. The problem gets worse as the car gets hotter. When I cold start, she runs pretty good. Car runs very rich (on and off) to the point where it burns my eyes and nose. I have lost power on the top end, maybe 3500-4000 (tach isn't accurate towards redline)

What I have done:
2 different MAP sensors
2 different TPS sensors
2 different ignition coils
2 different ICMs
Ohmd out injectors when cold - 15.xx. when hot - 17.xx
2 different computers
2 different dizzys
2 different cap and rotors

Info:
When this issue first appeared, it shook my car so bad that my CTS ripped itself in half. My trans mount bolt dropped out and starting shaking the trans. One plug wire found its way to a header and torched itself. I fixed all of these issues and still have my original issue to be done. My scans while driving have been unsuccessful in locating the issue and no codes while driving.

Mods:
Motor was rebuilt 13k miles ago.
Edlebrock headers
flowmaster exhaust
super 10 instead of cat
Injectors are 24# bosch from southbay

My thoughts:
I have not done spark plugs or all plug wires yet and I have those bosch plugs which everyone says is crap - they have 13k on them. I have not taken a look at the IAT yet. I want to do a relocation mod when I put the stock airbox back in. I was thinking this was an ECM issue but would it make sense that it gets worse as the car gets hotter?

I know I'm missing some information - I'll fill in the gaps as I remember everything. This is the first time I have not been able to solve an issue with a SBC right away!

 

Check your fuel pressure.

 

Have you taken a look at your EGR valve and solenoid? Common problem on any car after this many years. You said engine was rebuilt so maybe it was replaced, but I know I didn't replace it when mine was replaced and I've finally narrowed down a persistent problem to what I'm fairly sure is EGR related. Bad EGR can cause bogging, and I assume fuel problems as its pretty much a massive vacuum leak if its damaged.

 

Just an update, FP is fine and EGR looks fine. The car has been running better the last few days but after about 15 minutes or so, the car will develop this stumble in every gear at certain rpms. I have to keep feathering the gas on and off in order to go anywhere. When the problem occurs, I can tell right away as the perfect idle sounds like crap. Once I get past the stumble, it will run okay until it stumbles again in the high end. I'm going to do plugs and put some new wires on soon. Someone told me to swap out my IAT but I am going to try and be lazy by doing the relocation mod and seeing if I can unplug the connector without taking the plenum off - if I'm taking it off, might as well swap the IAT, maybe get an adjustable FPR while I'm at it too. Another idea I have it grounds, as the one that was suppose to be attached to the firewall was just hanging out behind the dizzy. It didn't fix anything though when I put it back on. The problem seems to be worse with a hot start but it does sometimes go away and come back. When I was out last night, it started to run PERFECTLY with power and all, but then started to run like crap after 5 miles on the highway. It was a fun 5 miles.

 

Your running 24lb injectors in a 305. Did you tune for that?

 

So like a dummy I check FP when the issue was not happening. The car completely died and I couldn't hear the fuel pump prime. It would only start when cold but didn't run that great. I check the FP when the issue was happening, 29 PSI at idle and when I pinched the return line it didn't rise at all! Time to drop a tank!?! I just wanted to update the post again because I see so many unsolved threads on TGO. I've been a lurker for a few years now. I'll update again and let you guys know how she runs and Nov. 16th @ Island Dragway is holding Christmas drag racing event so I'll be over there most likely to see how she performs.

 

Job done. Runs like a top again.
Can a mod mark this as solved?