Ok, so first off I drive a 2005 A4 1.8T6-speed stick. Oh and i have quattro. Anyway the car was in storage for the past month or so (1/4 tank of fuel, no stabilizer)I took it out and filled it up (93 octane) and the next day the check engine light came on. I got the code it's P0420, and the OBD II port scanner said that bank one was not performing efficiently. Is this bad gas? Dirty O2 sensor? I've noticed that i'm using a little more gas, but other than that the car is running extremely well. Anybody got any advice?

 

No, that means your cat it bad. You might wanna go to the dealer and see if there is a re-flash available for the ECM, a lot of cars throw these faults due to sensitive O2 sensors.