I replaced the cats with two new carsound ones and I cleaned the hell out of the MAF. The code has been gone since.

 

OK guys. Great discussion with lots of good advice. However, it sounds like the problem still exist for this guys and me too. I have been through all of the suggestions including replacing MAS and upstream O2 sensor, check for all leaks, clean injectors, new fuel pump, timing belt, fuel filter, etc and still getting P0171 code. Additionally my fuel mileage is half of what it was and the the engine is surging and stalling. Across the internet, I have been seeing a lot of people complaining about these problems. Has anyone heard of the systematic issue and does anyone have any other suggestions? Could it be the MAS sensor or the ECM?

 

Also, i have the same problem with the flat curve of the read out on the O2 sensor, though I know the O2 sensor is good. I replaced it and then replaced it with another just to check. I am assuming both new sensor weren't bad, but still getting the lack of fluctuation. Thx