I have a Sweet Audi 90 20v Quarto that wont pass DEQ its1991 and runs great small miss but nothing that is bad runs strong doesn’t smoke or use a lot of gas smells real rich black carbon on inside of tail pipe did complete tune up plugs cap rotor put it didn’t improve the results to much the only thing I left to change is the plug wires and catalytic converter or fuel injectors it has 219k on it but starts and runs great if I cant get it to pass DEQ I will sale it for what I have into it 1600. bucks help!!