I have a 1995 honda civic. The rpm gauge bounces back and forth every time I shift, or sometimes when decelerating. I replaced the coil in the distributor, the icm. What could be causing this behavior?

Loose wire, gauge?
A bouncing RPG and Bouncing RPM gauge are 2 different things. Good luck.

Did you clean and crimp the BLU wire on the ICM, that goes to the tachometer, as previously suggested?

If the problem persists, disconnect the BLU wire and tape it. If you can't live without the tach, replace it. A bad tachometer can short out the ignition system on these cars.