I have a 2000 cavalier 2.4, the car was working perfectly fine until I decided to change to a walbro fuel pump, now for some reason every time i change gears while driving the car accelerates on its own when I press the clutch to shift or even if I put it neutral...... the only thing I did waschange fuel pump....

If the car was running fine before, why did you change your fuel pump? Are there any other issues it's having when your in gear? Do you have an AFR gauge?

sounds like your air fuel ratio is not right maybe lean look into that u can damage ur engine or you went up in fuel psi and computer cant adjust your injectors enough

Ya buddy

how is the car accelerating if you're pushing the clutch?

try to describe your problem correctly.

I believe he means revs up. My 01 z auto acts similar. It tries to accelerate on its own and tries to rev to 4500 rpm in neutral but only above 5mph, once i slow down to 5mph it acts normal. Its not a vacuum leak, the iac or tps, or bad grounding. I do however have a problem with one of the wires in the harness near the fuel pump though and the OP's issue has me wondering if that's my issue.

I would double check all the wiring in that area and see if something is loose.