How to fix error code P0150,P1931,P0304,P0300 for this car? Model:A4; Maker:Audi; Year:2001

Hello, first, you did not mention which engine you have. Based on the first 2 codes, it must be the V6. There are engine misfires in there, as well as a bank 2 sensor 1 oxygen sensor concern. I am not seeing a P1931. Regardless, codes alone will not test anything. They only give clues on how to proceed. You'll have to check fuel and ignition systems for the engine misfire. I would do that first and then go from there as far as the other two codes go. Some codes happen as a result of other concerns that set other codes. So an overall in person evaluation of the vehicle with proper test equipment, technician experience, and shop manual reference materials are quite important to the process of finding out what is wrong with your Audi.