Grand Prix :: 1997 GT Running Extremely Rich And Pressure Build Up In Fuel Tank

I'm having this weird problem with my car, 90% of the time it will start to run rich, until it reaches normal temp, to the point that I can smell it coming out from the exhaust. LTFT is at around -15% and it seems to go down after cruising for some time but will go back to negative at idle. My first suspect was the FPR so I checked it and found no gas smell on the vacuum hose, then I decided to run the engine with the vacuum hose disconnected and see if any fuel would come out, 5 minutes later and it was still dry.

There is a chance that the MAF sensor is bad, I'm 90% sure it is, because it will sometimes read 2.9-3.1 gps at idle and according to the rule of thumb of 1gps per liter of displacement, it shouldn't go that low but I might be wrong about it; I disconnected the MAF and the smell was still there, today while driving it was reading 5.45gps (A/C was on) and the smell was still present; car also feels sluggish from time to time only at normal operating temperature (which I assume is because of it running rich).

There is also a vibration felt through the steering wheel only while idling in gear at all temps. Today when I got home and after I turned off the engine I heard a noise like water was running. It was coming from the car so I tried to find where the noise was coming from and it's from the fuel tank. I removed the fuel cap and lots of air came out (or sucked in?). I reinstalled the cap and pressure started to build up almost immediately! I have a video, which I'm sharing, so you can see what I'm talking about; I was even able to hear the fuel tank expanding because of the pressure inside, not sure if you can hear it towards the end of the video (when I put the phone under the car). [URL] .....

It also happened today that I was cruising and the engine hit the rev limiter after I stepped on the gas (WOT) to overtake another car. I immediately removed the foot from the pedal and gave it less gas and it acted normal, no slipping from the transmission at any other time. There is one more thing that I'm not sure about it. Every morning, the engine will sputter for 1 or 2 seconds after starting it but it will be fine for the rest of the day. I once tried disconnecting different sensors from the engine and the only one that seemed to make a difference (it didn't sputter) was the TPS.

Things done so far:

- I replaced the EVAP purge solenoid (P0441 was present) back in february.
- Rubber pieces at charcoal canister also replaced, old ones were rotted to the point my hands would look black just by rubbing against the hoses.
- Upper intake manifold was also replaced by me in november last year.
- New NGK spark plugs and OEM spark plug wires last december.
- Cleaned the MAF sensor with MAF cleaner, no dice. Used brake clean, no change. It's a reman Cardone from autozone, which tells us it's 90% sure it's broken.
- New Duralast MAP sensor back in 2010 because a mechanic broke the original.
- 10qts transmission fluid and filter replacement 2 weeks ago.
- Fuel pump was also replaced back in 2009 maybe, can't remember the exact year. The old one would start making some kind of a hissing noise after prolonged driving.

NO DTC'S PRESENT. I once checked Mode $06 data with a mid-level scanner I have (AutoXray EZ-scan 6000) and saw a test had failed, I think it said something about the MAF and EGR. IHaven't connected my fuel pressure gauge tester. Since I can smell it running rich, I didn't think it would be necessary. I'm thinking that there could be a problem with the EVAP system that's causing the excessive pressure in the tank but I'm not sure what that could be. Is there any chance that the pressure is also causing the rich mixture?