starts up every morning no problem drive to work go out for lunch starts fine 1/2 hour later will turn over but won't fire up. does this often. Then it will start out of the blue. Did that more often then i care to say. but yesterday it stalled while I was driving and I could not get it to start again turned over fine. It happened once before and when i had it hauled to a gaarage and it started right up once it got there

what kinda grand prix...SE, GT, GTP? and what motor 3100 or 3800? also, how many miles?

sounds kinda like a crank sensor