My buddy has an 01 A6 with the 4.2 in it. He is currently getting these codes:
P0101 - Mass or Volume Air Flow Circuit - Range/Performance A
P0130 - O2 Sensor Circuit - Malfunction (Bank 1 Sensor 1) A (o2 sensor)
P0174 - Fuel Trim - System Lean (Bank 2) B P0150 - O2 Sensor Circuit - Malfunction (Bank 2 Sensor 1) A

It sounds like a MAF and a couple o2 sensors but I am not very familiar Audis. Any help is much appreciated!

 

You are correct. Mass air flow and an O2 sensors, the lean condition is most likely related to the MAF, but could also be a broken vacuum line.
Are the faults sporadic or hard faults?

 

Explain? He reset the codes took about a day to come back. Does that help?

 

Sounds like his MAF sensor is going bad as well as 1 O2 sensor.

I would definitely bet that the MAF failing is causing it to lean out because the ECU is confused on what to do. As Tommy said it could also be a broken vacuum hose/fitting. I ran into this at one point but it was also causing mis-fires.

Did all the codes come back after the reset? Are these the only codes?

 

I am not sure if all codes came back these were the only codes when he first read them. I appreciate all the help.

You think we should do the MAF then see if it comes back?