One problem related to engine has been reported for the 2000 Audi S4. The most recently reported issues are listed below.
Drive by wire (dbw) throttle body system failure. Ecu throws epc code and engine power is compromised. Car may be unable to exceed 40 mph and car may buck uncontrollably. Restarting car may clear condition for a short time. Traffic negotiation was quite dangerous, as dbw system may error at any time. Dbw throttle body seems to be an answer to a problem that does not exist.