One problem related to manifold/header/muffler/tail pipe has been reported for the 1999 Volvo S80. The most recently reported issues are listed below.
Contact states: on 7-8-05 while driving at 25 mph the consumer heard a sputtering, and all of a sudden there was a burst of black smoke coming from the fuel pipe. Had vehicle towed to the dealer. , who could not duplicate the problem.