I just bought an audi a6 and the previous owner told me the only problem with the car is the mass flow sensor which causes a bad fuel economy. I ordered the part and put it in. The engine light turned off and the car was working fine for a few hours. Then all the sudden the sudden light turns back on and it starts burning fuel extremely fast again. I'm not sure what the problem could be I was wondering if any of you guys could help me here.
I just checked it's averages 9 mpg.

 

Did you get the code for the mil?