Help With Car Quitting!!!!

hey everyone....over the last two days, i would be driving my Shadow and after a little while when the engine gets warmed up, the car would just turn off as i was driving....any idea what may be happening?? i took it to the shop, and they couldnt find anything wrong with it....it did this 8 times yesterday and 3 times tonight, and it is getting very hard to drive when i have to restart on the middle of the highway....if anyone has ever experienced something like this, let me know so i can tell the repair guy and get it fixed.

thanks!!

y2k

my 88 lebron 2.5L did that and i kept re-starting it .then finley the bottom plully fell off and it quit .got it put back together and it was fine . turned out the bolts came loose