It's showing idle at about 500rpms and when i'm running 60mph it's only at 1,000rpms and it should be around 2,000. how do i fix this?

 

Gently pull the needle back off of the tach and reset so its correct.

I used AutoTap to read and set my needle back to where it was supposed to be after my overlay install.

 

what is autotap????

 

It's PC based OBDII scanning software, it allowed me to see the RPM that the onboard computer was reading, I fiugred this was as accurate as I was going to get.

Autotap Website

However, you aready know about how much the tach is off, so you should be able to guesstimate how far to move the needle. It may take a little longer to get it right though.

Just noticed that the original poster is running a ODB1 computer... Sorry about that, there are other options for pulling the RPM from the computer for those cars.

 

Thanks guys. guess i'll pull it all back apart and drive down the road, stopping and resetting the needle until i get it right.