I recently bought a 97 z28 A4, one owner 74k miles. The old man had simply drove it back and forth to work. I noticed where the water pump was leaking and promptly changed it, as well as put new plugs, wires, fuel filter, and elbow and moroso intake on it. I also put the march power and amp pulleys on it as well as had a wait4me performance tune done. I had them delete the rear o2's and air injection as the man had deleted the rear converter because it was rattling and the smog pump due to an air injection code. I also noticed where he kinked the fuel line by routing it behind the master cylinder. I put new lines from the rail to the metal line under the car, yet I still have a bank 1 and bank 2 system too lean code. Please help as I have reset the codes and it will come back after a few miles. Any Ideas as I am new to the LT1 scene?

 

check for exhaust leaks and or vacum leaks! I am running into sort of the same issue but im not throwin codes. Scanner is showing +15 fuel trims at idle. In your situation the lean condition is so bad the fuel trims can't correct, which is causing the code. Also could be a fuel pump issue or simply a fuel filter!