My 2005 s4 is running so rough that its not drivable. Scanned it and I got a camshaft sensor error. A reputable German car mechanics shop says it sounds like there's a mechanical problem within the engine. Car has 122,000 miles and had coilpacks replaced about 8 months ago. When I scanned car a few weeks ago it said misfire cylinder 8. All of a sudden it started running fine. Two days later I experienced my current problem and had car towed...had no power at all and after revving to 4 thousand rpms engine made a strange loud rattling noise..any thoughts???