lately ive run into an issue with my 1992 pontiac firebird with a 3.1l GM 60 degree engine.
Open loop:
-Initial start up is quick with RPMS reaching 1200-1500 then quickly dropping to 1k at park idle and around 800 in drive idle.
-Under forward acceleration reaching near 2.5k-3k rpms she will surge with rpm spikes of ~+500rpm and accompanying pop of the exhaust.
-Acceleration is weaker than it was before.

Closed loop:
-Once operating temp is reached surging stops
-Acceleration is better but not perfect.

Overall:
-Acceleration decreased
-Fuel mileage decreased

Recently replaced parts:
-Distributor cap, rotors, wires, and ignition coil

Current checklist:
-Spark plugs
-MAP Sensor
-EGR and hose
-Fuel Pressure

Thats all i can think of currently that may be causing issues that i need to check. If anyone as any other ideas that may be of use i would greatly appreciate the help.

 

New fuel filter.

 

fuel filter has been replaced within the last year give or take but its a cheap enough part to replace without much thought.

 

I wonder if the catalytic converter has broken up and clogged- but I'd think acceleration would be horrible... e.g. pushing on the gas and nothing really happens. Could the ignition timing have slipped?

 

Backfiring out the exhaust implies lots of unburned fuel in the exhaust - so either misfiring ignition or too rich.
Since it gets better after it's warmed up, I don't think it's ignition.
After it warms and enters closed loop, the O2 sensor helps the ECM to find the correct fuel mixture.
So I think it's running very rich and the O2 is helping to mitigate that when closed loop is achieved.

Do you get any check engine codes?

Some possible causes of rich mixture include
vacuum leak in the hose that leads to the MAP sensor
vacuum leak in the hose that leads to the fuel pressure regulator (it should be referenced to manifold air pressure)
Check electrical connectors, look for anything broken that might not be making good contact.
Leaking fuel pressure regulator - try sucking on the hose that goes between the manifold and the FPR. If gas comes out, the FPR is leaking and needs replacement. Don't swallow gas, use a vacuum tool if you prefer.
leaking fuel injector - see below (fuel pressure check)
bad MAP sensor - if you unplug the electrical connector from the MAP, does it run better? If so, the MAP is suspect. But make sure it's getting good vacuum first, otherwise it can't ever work correctly.
There's more precise ways to check the output of the MAP sensor involving either datalogging the ECM, or measuring signal voltages, but I don't have data about what voltages to expect.
I don't think MAP sensors fail very often.
bad coolant temperature sensor - on a Fiero, this sensor is a variable resistor. The resistance between the 2 terminals changes according to the temperature. At 40F it's about 7500ohms, at 70F it's about 3400ohms, at 90F it's 2150ohms. If you have a multimeter, try measuring the resistance on that sensor at some known temperature and see what it says. If you don't have a multimeter, you should.
My experience is with the Fiero but the Camaro 3.1L with 7730 ECM uses a very similar setup. I'm pretty sure the temperature sensor should work the same as I described, because people swap 7730s into Fieros without needing to change that sensor.
You can also "force" a given temperature by plugging a resistance into the connector, taking the place of the sensor.
Make sure you are looking at the sensor that communicates with the ECM, not the dashboard.
bad intake/manifold air temperature sensor - same as above, but I don't think the ECM reacts as strongly to this one. The coolant temp sensor is more critical. If both are working they should read about the same resistance on a cold car.

If you have a cable that lets you plug a laptop with datalogging software into your ECM, you can see all the sensor readings directly to see if anything looks wacky. Sometimes that can be a quick way to narrow down the problem.

Fuel pressure check - fuel pressure should be about 40psi with key on, engine off. With engine started and idling, fuel pressure should be slightly lower. If you open the throttle, fuel pressure should increase slightly. Fuel pressure should move in relation to manifold air pressure, which increases when the throttle is open.
Now turn the key off. Fuel pressure should hold. If it drops quickly then something is leaking - likely a fuel injector. It's normal to lose a few PSI in 10-15 minutes.