Two problems related to engine and engine cooling have been reported for the 2004 Audi S4. The most recently reported issues are listed below.
Car engine was misfiring - was informed a faulty coil pack was causing the issue. One week later the misfires started again. Two more coil packs were replaced. 2 weeks later another misfiring episode. Car died at intersection so was towed in for inspection. Camshaft adjuster/cam guides had failed. Parts were replaced for 5k and then 2 weeks later cylinder 3 failed when valve and piston interacted - car died again on the highway. Car engine is going to need total engine replacement.
2004 Audi S4, build date 09/03 : 1. 24 Aug 06- 16,500 miles- a/c stopped working- replaced entire a/c system (compressor, hoses, pipes, drier, restrictor) under warranty. 2. 10 Apr 07- 23,253 miles- car won?t start- starter replaced under warranty. Pealing shift knob (chrome surround was pealing and the edges were like a razor blade), replaced under warranty. Center console latch broken- replaced under warranty. 3. 22 Feb 08- 31,992 miles- engine replaced due to faulty valve seat. Seat broke allowing valve to be sucked into cylinder and then punched out the side of the block. Engine replaced under warranty. 4. 10 Sep 08- 37,448 miles- a/c stopped working. High pressure switch replaced under warranty.