RPM surge issue 96 Grand Prix SE

[Dustindell]

When my RPMs hit 2200 the car looses power and the RPM jump violently up and down between 1500 and 2200. As the motor warms up the RPMs hold good longer but start jumping at 2500. When the car is fully warmed up I have no issues what so ever. The car never acts like it's going to die and if you feather the pedal the car will gain speed but slowly. This only happens when the outside temp is 40 or colder. I let the car warm up today for 20 mins since it was 25 out and there were no issues. Anyone have this issue? I did pick this car up on the cheap to save gas and it is doing a good job of that. Also when I'm sitting at a stop light and it is in gear there seems to be a growling that can be herd in the car and felt in the brake pedal.

Thanks

[02NavyBlue]

Any codes? Maybe an o2 sensor isn't reading correctly, or a partially clogged cat? I'm guessing it's the 3.1, I'm not too familiar with pregens. The growling would have to be diagnosed with someone replicating the problem, and going under the hood to find the noise. Growling is often power steering pump noise but that's usually obvious when turning. Maybe it's the transmission pump. Check the fluids.

Anybody got any better ideas?

[Dustindell]

Yeah 3100 motor and not throwing any codes.

[02NavyBlue]

Seems like an o2 sensor would be at fault, like the heater circuit isn't working (which enables it to work on cold starts) Once the exhaust warms it up it works as intended. But I know on 97+ GP's it would throw a code, idk maybe the pregens don't?