99 Monte Carlo stalling

[Bellewiccan]

I have a '99 Monte Carlo with a new Jasper engine in it. The problem is that it keeps stalling. I have read the posts on here and did replace the EGR valve but the problem is still occuring. When stopped at a stop light the RPM's will go way up then crash way down. I know then that when I try to push the gas to go when the light changes that the car is going to stall. Sometimes, when in park but still on the car will rev all the way up to 4500 rpm on it's own without me touching the gas pedal at all. I am beginning to think on terms of the movie "Christine"! What else could be wrong? I would like for my husband to fix it himself instead of having a huge mechanic bill since I just spent all that money on the new engine. Any help would be great!!