Warning, text wall.

Guys, I've looked all over the internet, mostly on this website. I am at a loss as to what to do here. I bought a 1991 Firebird 3.1 base in December. My city is yelling at me to get rid of it or get it running. I have replaced the following:

exhaust from the y pipe out (including Walker cat and Magnaflow muffler)
oil and filter
spark plugs and wires
distributor cap and rotor
fuel pressure regulator
various vacuum lines

When I first got the exhaust in and tune up done it was hard to start, it would surge up to 3000 rpms and then die immediately. I would have to bump the throttle to keep it alive. Once warmed it would surge constantly back and forth between 1k and 2k rpms.

I discovered fuel in the vacuum line to the fuel pressure regulator. I then tore the intake plenum off and replaced the fuel pressure regulator (previous one had some rust build up but the diaphragm looked fine). Cleaned the throttle body and idle air channel. Intake plenum bolt sheared off putting it back together. Managed to extract the bolt. All new hex head bolts and washers instead of flange bolts. It would then idle at 2500 rpms, bump the throttle and the idle raised to 3000 rpms.

I drove the car to my friends house today. Sprayed the vacuum lines with starting fluid and found nothing. Sprayed around the intake gaskets, nothing. Then we tested the throttle position sensor. It reads 0.97v closed and 4.5v open. Smooth increase and decrease in voltage with moving the throttle by hand. We then tested the idle air control valve. When the engine is on and it's unplugged and removed its halfway out, when the engine is turned off the pintle moves all the way out. We then tested the MAP sensor. It reads 4.97v with no vacuum and around 1.1-1.2v at 20" of vacuum. Managed to pull the vacuum line to the fuel pressure regulator and found a lot of gas in the line again. I followed the vacuum line and it was T'ed off before the charcoal canister "Air" nipple with one hose ended up dumping in front of the wheel. This hose was absolutely covered in soot. This seemed wrong to me as this would prevent the fuel pressure regulator from operating under vacuum. The purge valve is hooked up to a T that goes to the throttle body and the other line T's off again, both lines go to a valve that leads back to the fuel tank. I disconnected the T leading to the Air nipple and plugged it and I disconnected the T going to the purge valve and plugged it. I sucked the gas off of the top of the fuel pressure regulator. The engine was able to start and idled much much better but too high. We adjusted the idle screw on the throttle and got the idle down to 800. It sputters a bit between 600 and 800 and eventually dies and backfires. We took it out and drove it around and the thing wants to drive itself. If I hold the brake it dies. It won't handle going under 1500 rpms. I drop my friend off and drove it home and when I parked it the idle was again 3000 rpms. I have a new idle air control valve coming tomorrow but I'm not sure that it's bad. All measurements were with a fluke 114. Thank you for any help.

Edit: when the intake plenum was off I tested the resistance across all six injectors to be 12.5 or 12.6 ohms on every one of them.

 

Hi Joiner, In reading your post two things struck me about your problem.

#1, Never, ever, is there supposed to be fuel on the vacuum side of the regulator. If there is, then it's leaking, even if it's a new one, and that has to be addressed before any real troubleshooting can begin.

#2, You talk of vacuum line weirdness, as if perhaps some previous owner messed with it. If each and every vacuum line is not as shown in this diagram, you must also correct that before attempting any further diagnosis.

 

I apologize, I never saw any notification that there was a reply to this thread. Update: replaced the idle air control valve, replaced the throttle position sensor, corrected vacuum lines. The vacuum line was sucking gas up through the vapor canister and that's why I had fuel in the lines to the FPR. This also caused lots of gas to be inside the vapor canister. Engine currently starts up and goes to 1500 rpms, slows down to 800 when warm and has a slight stumble. After heated fully the idle drops to about 700 and gets rough. When put in gear it will eventually die. Replaced the EGR valve. I replaced the O2 sensor today. We also pulled the distributor cap and found 5-6 degrees of slack on the timing chain. Double checked the new FPR by putting a vacuum on it. It held 17 in Hg for 20 minutes with no additional fuel coming from the vacuum line. We found small holes in the EGR tube from arcing the back of the alternator. Patched those today. No different. The idle of 3000 rpms earlier was from a loose throttle adjustment screw, replaced that. One of the vacuum lines that wasn't hooked up at all was the air pump, hooking this up stopped backfiring. Also attempted plugging the vacuum line to the brake booster and no change was found.