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....

It's not possible for it to accelerate if the clutch is disengaged. So you must mean the RPMs increase.

Changing the fuel pump did not cause the problem. If you feel that caused it, then switch back to the stock pump, which was working fine. If you don't want to switch back, you need to find out if the RPM increase is caused by a mechanical or electrical reason.