I have a tach on my 96 SE that has the jitters. It goes haywire when the car is started, but the speedo is fine (95% of the time, just needs a tap to get it working). I've opened the cluster and tightened the screws at the back but the tach still is haywire. I read most of the posts here and was wondering whether it would be worth trying a new VSS even if I'm not getting a 500 code for a bad speedo. Odo works fine too. The circuit system at the back of the cluster is not a solid board but a flexible "thingy".

 

Had similar issue with tach (always point to redline). Try all suggestion, did not fix it. Pull cluster at local JY. No problem since. Replace either whole cluster or just the tach.