99 Passat problems

I need some help. I'm getting real sick of my stupid car! it's been in the shop for about 3 months and noone can figure out what is wrong. when i'm accelerating from a stop sign or something. my car just jumps instead of going it continues to jump through the intersection and if i'm lucky it will then start going. then it just happens next time i stop. i've replaced the coils didn't help. the onboard computer isn't giving out any codes. no check engine light on. everytime i take it to the mechanic it doesn't act up for them. i've left it for them to drive for a few days and they still can't come up with anything. Has Anyone had this problem before? any suggestions would be greatly appriciatted

Update:
Finally an answer. Sort of. My car is getting to much fuel and not enough air. The mechanics are stumped on why this is happening. Has anyone experienced this problem.