95 rivera rmp flux

I have a 95 buick rivera and when I am in gear and stopped you can feel the car acting like it wants to die, it does not die but you can see the rpms flux. If you put it in neutral it will idle just fine. I think it may be the crank shaft postion sensor. I had the harmonic balancer replaced and since then it has acted like that. I also he something make a weird noise in the s/c. Any one that can help will greatly appreciate it. Thanks

Dwane
(yankee387)