I have a 2007 RS4 Avant with a complete miltek exhaust system, including 100 cell racing cats. I brought the car like this. It has all of the correct engine mapping within the ECU's, as I have had this re-mapped myself. I have had problems in the past with fault codes pointing to lambda sensors, which turned out to be the inlet manifold. However, I am now getting the emission warning light illuminating at various times. The fault codes I am getting are, P2097, post catalyst fuel trim system to rich, bank 1, and on separate occasions, P2098, post catalyst fuel trim system to lean bank 2. I know this is a long shot, but can anyone advise. Thanks.