I recently picked up this '90 IROC Convertible with the 305 TPI, all stock.

When I got it, the tach was not working correctly. I start the car and the tach goes to zero then all the way over 7k RPM.

I checked all the wiring and all seems fine.

Any ideas on where to go from here?

 

Seems to be an issue with these cars, look around on the site and you'll find a lot of tach problems. Mine doesn't peg at 7k, but its way off. about 800 rpm off at idle and almost 2000 rpm off at 3500!!!

 

I looked around the site but nothing helpful that I found about trouble shooting.

Any one have a '90 wiring schematic?

 

https://www.thirdgen.org/forums/elec...meter-fix.html

Its a sticky in the electronics section if you're looking for it later

 

heard of the VSS going bad. dont' know for sure, but i'd read up on it.
(my 92 z28 convert is also erroneous tach rpms and speedo) I've been using my cell phone - speedometer application until i get it fixed.

good luck-