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I've been and still am searching, but any help from the 'Hive' is always greatly appreciated. My wife's 2001 NB has only 79k miles and has always been pretty reliable, but has also always had its CEL illuminated. We threw $800 at it at the dealership before I called it quits and they could not find an issue- although they were very eager to keep replacing components! Anyway, the normally smooth engine has begun missing a little, there is now a noticeable hesitation between depressing the accelerator and the engine's response and wife said that it stalled at a red light the other day. About a week ago she stated that it was running rough so I threw the scanner on it and found two codes, P0103 (Mass or volume air flow A circuit high) and P0172 (System too rich bank 1). Her air filter was a little dirty, so I replaced it, cleaned the MAF, cleared the codes and it ran fine for about 3 days. Now it is running worse and has stalled so I again checked and the following codes were stored:
P0103 (Mass or volume air flow A circuit high)
P0172 (System too rich bank 1
P0139 (Slow response bank 1 sensor 2)
P1127 (Manufacturer control)

I'm looking in several directions and have followed threads regarding vacuum leaks and the Fuel Pump Relay (#409) issues. I didn't know if these codes (some of them repeats) in conjunction with one another might throw the 'AH-HAA!" switch in someone's head. As always, any guidance is greatly appreciated- I'm growing dangerously short of patience and beer...
 

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P1172 is for too rich, long term fuel trim:

P1127 Volkswagen Long Term Fuel Trim B1 System Too Rich OBDII Engine Light Trouble Code | Engine-Codes.com

My guess is that the either you weren't effective at cleaning the MAF sensor or it is going bad. There are wires kind of deep inside it that need to be cleaned. Look at the second message in this thread to see what needs to be cleaned:

GenVibe - Community for Pontiac Vibe Enthusiasts • View topic - How-To: Cleaning MAF (Mass Air Flow) Sensor

It is for a different kind of car but the parts are very similar in construction. It could be the part is going bad as well. There is an electronic circuit built into the MAF.

Ideally you could hook a scan tool up and monitor the MAF in real time to verify its operation. Look at the third post in this thread for info on how to diagnose the MAF with a scan tool.

http://newbeetle.org/forums/2-0-liter-gas/59939-definitive-aeg-maf-test.html
 

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This is other one of the lets slow down a moment situations.

1. RARELY does a car actually run Rich. Many times Rich conditions are due to bad sensors and false data.

2. You have a scan tool, does is read and display real time data?? If so we need the following info:
1. Long Term Fuel Trim at idle
2. Engine coolant temp after at least 10 minutes of driving at idle.
3. What is the history on your current MAF? Is it original? Is it a replacement?
4. If your scan tool will display engine load, display engine load and see if the valve jumps over 100% under heavy throttle in 2nd or 3rd gear.
5. What is the status of the O2 sensors? Are they original?
 
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