2002 v70 intermittent starting issue

[dcvh]

car starts... runs momentarily then immediately dies 4-5 times a month..it will restart after waiting anywhere from 5 min to all day...happened again today..only this time i restarted and very quickly put it in reverse and it continued to run to my amazement...just make sure it wasn't a fluke i did it all again..restarted without putting it in gear.. it died immediately.. restarted. put it gear and it continued to run

my mechanic tells me it could be any number of things

ant ideas?