virex21

Hi everyone,
I'm hoping someone with more mechanical knowledge than myself can help point me in the right direction for an ongoing issue I've been having with my car. I have a 2006 Audi A3 3.2L Quattro Sportback (8P), 125,000 miles, with service following the Manufacturer's Maintenance Schedule. The issues with the car include: intermittent rough idle, intermittent lower fuel efficiency, sometimes it smells like raw unburnt fuel while idling, and I also perceive a slight loss in engine power at times. There is also some engine vibration at times while at idle. The gas smell is only on the outside of the vehicle and not inside the vehicle cabin. The codes my OBD2 Scanner has pulled collectively over the last year include:
P2273 Oxygen Sensor Signal Stuck Rich Bank 2 Sensor 2
P2198 Oxygen Sensor Signal biased / Stuck Rich Bank 2 Sensor 1
P2099 Post Catalyst Fuel Trim System Too Rich Bank 2
P0174 Bank 2 System Too Lean
At no time did all of these codes occur at once.

I've taken my vehicle to the dealership on 3 different occasions to get it diagnosed. To date, I've replaced the MAF, had a fuel injector service, ran some fuel treatment through the gas tank, had the stealership inspect for vacuum leaks, and check the wiring of the 02 sensors among whatever other computer diagnostics I'm hoping they did. They stated the last time they thought it was most likely a bad ECM(PCM), which I am extremely skeptical about. I did have a faulty oxygen sensor bank 1 02 sensor 1 (upstream) replaced at 75K miles due to it going bad. I have not replaced the other upstream oxygen sensor.

This problem is driving me crazy due to it being so hit or miss. Sometimes the car drives great upon a cold start, while other times it idles rough. One thing I have noted is the impression of something being "stuck". What I mean is at times I am getting much less fuel efficiency than I should be, so I will punch the gas pedal down while driving then release it, and voila, the gas mileage readout that displays your current MPG will go back to where it should be (from 16mpg on a flat road to ~26mpg). I've had this car for 8 years, so I am quite in tune with when it is running properly and when it is not. Could this be as simple as a failing 02 sensor and maybe the few times I brought it into the dealership they didn't look at the Fuel Trim data to see if the 02 sensor was failing/sluggish? Is it a bad EGR? I really have very little knowledge of cars so I am just kind of throwing out the things I have been reading online. Anyways, I know this may be long winded but I am determined to fix this issue. Any insight is greatly appreciated!

Thanks - Rob