Quote Originally Posted by christianb5s4 View Post
Thankfully I can say this has been finally solved. I had the high pressure fuel pump replaced as there was some evidence it was leaking oil slightly and leaking internally. At the same time, all EVAP lines were double checked and verified there's not a single leak. So we went back to the basics, checking out stock Audi photos of the C6 3.0T engine bay and discovered the cause.

The EVAP line that should connect to the purge valve was connected to the intake and the PCV line that should connect to the intake was connected to the purge valve. Doh. Whoever worked on the car prior to my ownership put them on the wrong way around. No codes at all, car runs and starts smoother, power is more linear, gas mileage is up and I filled the tank and had no issues starting after fill-up.
I just want to thank you for posting this and saving my sanity. I work at an european independent shop and we've been battling this code for years, customer has just dealt with it until it was emissions time. We've had the intake / supercharger off multiple times and each tech put the hoses back the way they saw them (which was backwards just like yours).
I owe you a beer man, and this just shows how important it is to document what you do and keep good notes. By you taking the time to post this you saved me.
I miss my B5 S4 everyday