Do you fellas think that's one of the crank position sensors, or the tach itself? Motor runs fine even if tach goes to zero rpm or lower than actual....

 

My dad had a similar problem in his 3rd gen. All he did was swap in a new one from a Junkyard and it worked fine. He even got the odo reprogrammed for his milleage for like $25 lol.

I believe you can also re-solder the loose connections on the back of the cluster to fix its issues.

 

You need to replace the tach and your issue would be resolved. Many threads on this issue which is why people did not respond.