Wilkinshc

Thought I would pass this on in an effort to help others. I have a 2012 Grand Sport A6 with the Hennessey HPE650 kit (basically Edelbrock supercharger and headers). No changes to the setup at all. Start getting Engine light with P0171 and P0174 codes. Bought new O2 sensors, Maf sensor, checked for vacuum leaks and found none. Noticed when the car sat for a day or 2 over the weekend it turned over slowly at first. Ended up replacing the battery. No codes after the battery change so I put back in the old MAF and O2 sensors and still no codes. Been driving for a couple of weeks and still no codes. Seems a poor battery was the problem.

Hope this helps someone else.

extrapilot

You've learned that our cars like a very healthy battery, as others have had all kinds of mysterious things happen not knowing that the battery was near dead.
I caught by chance a border line battery by load testing it at work and after consideration I changed it for a new one. Even the engine cranked much faster afterwards..
This is usually the first highly recommend thing members here advise when posters discover electrical issues.
Good that you found your problems are gone ....thanks for the post..