One problem related to engine stall has been reported for the 1999 Volvo S80. The most recently reported issues are listed below.
On September 10, 2005 at approximately 2:30 pm, my engine abruptly stalled while traveling at highway speeds with cruise control engaged. I pulled the car off to the side of the road. It would not restart. Upon each attempt to restart, the engine would actually run roughly for 1-2 seconds and then stall. I had the car towed about 35 miles to my Volvo dealer. When it arrived, it started. This is the second time this has happened. The last time, the dealer found no problem. I am aware that Volvo suspects the throttle body in these matters. Mine has already been replaced!.