engine dies

My voyager '97 (3.3 L) suddenly dies while driving in the highway. After a few tries it starts again. This has happened seveeral times a month.
I checked comoputer code: 54.
I just had a tune up about four weeks ago. It was doing this before the tune up and it continues doing this after the tune up.
Any suggestions ?
Thanks

i had this same issue, it turned out to be the map sensor...hope this helps if ya havent already sold or fixed it.