I've gotten this problem now with my 92 RS and am needing some input on the problem... It seems now when I go down the road with it and hit a bump the speedometer and Tach needles start jumping around all over the place and then settle back down.. sometimes they do it at random...
I've had the cluster out of the dash 2 or 3 times and still haven't figured out what the problem may be... I'm thinking that it may be either a bad ground or its not getting a good connection in the back of the cluster?
I'd like to get some input on this to see if there is something I may be missing here.. I've made sure that the cluster has been properly installed back in its place and its still giving me this problem...
Thanks for the help!

 

I'm having the same problem with my tachometer - it started doing it when the weather cooled down, and I can't find anything that consistantly causes it to jump... seems to do it more when I'm taching low in 4th or 5th gear, but I could be mistaken. I'd love to know if anyone has had this problem and fixed it.

 

Ok - I did some looking around, and it looks like the main causes for this are bad plug wires, bad coil wires, or a bad coil... I just replaced my plugs, wires, distributor cap and rotor (like, 3 days ago) and got it tuned and timed right, so I'm gonna check my coil and see if that does it... but it sounds like yours bounces exclusively when you hit bumps? I'd guess bad wiring somewhere... if you're sure your gauge cluster has a good connection, no rust or anything, I'd suggest testing the wires to those specific gauges to make sure they aren't your problem... it really sounds like a loose connection somewhere though.