My tach over reads badly whats the cure?

 

It could be from a v6 car and is off because of that. The tachs are different between v6 and v8 cars. We really need some kindve info about the car and when it started doing this for us to even help you.

 

The car is an 89 iroc 305 tbi.

 

I got an '89 5.7tpi
and its doing the same.

 

i was watching a story on tachs on 2 guys garage, they said if your tach is going out, it will start to read higher than it should first, then go out later

 

Its not the tach. There is a small chip that is not operating correctly. You'll need to solder in some resistors to correct the high reading. But given the fact that you have a v6, Im not too sure if the repair can be applied.

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

 

I just saw that you posted 89 IROC 305. So go to the provided link and follow the instructions. Good luck man.

 

Repair instructions are for the troublesome 90 -92 tacho