Sometimes while driving the tach will stop working. However it will not settle all the way down to the peg, it will hover...like it is at 100 or 200 RPMS. The car drives and starts fine. If I shut it down and restart it the tach comes back.

Any ideas?

Check the wiring connector at the ICM (ignition control module) Remove the connector and clean with contact cleaner and apply dielectric grease to the connector pins before installing it back in place.