car dies while driving

Have 1996 Passat TDI with about 300,000.  Cars runs great, but lately while driving it dies,
or stalls.  All electrical seems to be fine.  All lights on dash are OK. but it does not restart
right away, sometimes I have to sit for up to 5 minutes, than it will restart.  It dies/stalls at
different times.  Sometimes 10 minutes after starting, sometimes an hour, sometimes
weeks, sometimes when idling. all fluid levels OK.