On my new-to-me 1998 LeSabre Limited.
Tachometer goes bezerk as soon as i start it up. All over the chart.
Any suggestions?

 

the tach signal is fed through the ICM, you could try to clean the harness that goes into the icm. if that looks clean, you can check the resistance between the icm and the pcm. should be at or close to 0 ohms.





but you would need a fsm to find the pinouts on the icm side. im pretty certain the white wire on the icm harness is the tach feed.