1989 Chevy Camaro Did some work on car. Now it dies right

The car is an 1989 350 camaro (TPI).
I installed an Adjustable Fuel Pressure Regulator and the car stopped running (it will start, but it is almost impossible to keep at idle, it is possible to keep it reved above 3500 rpm). To install the AFPR I unscrewed 8 bolts that hold the plenum, raised the plenum, unplugged the plenum temperature sensor and then unscrewed the 6 screws that held the original Fuel Pressure Regulator. I reinstalled everything back. No vacum lines, no sensors/connectors/wires were left out. Everything is plugged back in. After the failures I REINSTALLED THE ORIGINAL FUEL PRESSURE REGULATOR but the car did not go back to the way it was before. I went a few times back and forth but still same problem. Originally the pressure on the old regulator was low, although I did not measure it correctly (vacum line was on and it should have been off). Anyways, it measures 32psi. It is supposed to be I believe 44psi. A lot of people have the adjustable regulator and raise the pressure to 50 psi with no problem. In the end I kept the adjustable one, but whatever the pressure, whether 32 or 50 psi or in between the car won't run. I had to drive it back home after having it sit in my sister's garage for 2 days. I drove it on highway, and after about 3 minutes I got trouble code 44 (lean fuel mixture). I'll admit that I broke one vacuum line while working on the car but I replaced it. Oh, when idling (hard to do but when playing with the gas padal it's possible) the engine backfires a LOT. Again, no vacuum lines, electric plugs etc are unplugged. I belive some sensor might have died, but I got no idea where to look. I know this is a long shot but please tell me where to look. I am bad at electric stuff so if you tell me to test some electric stuff then please be specific. I had a full tune up/maintnance done a week ago (wires, spark plugs, cap, rotor, timing, air filters, oil filters, oil). The car ran like a wonder after the tune up. Please HELP! Oh, I don't know if this has anything to do with this but the oil pressure sensor went haywire. It just all of a sudden goes up, or down whenever it feels like it and also the engine temperature gauge goes all the way up the moment I crank the engine. This was not happening before I started the crazy AFPR project. Thank you!