In addition to my A/C issues in my other thread I just started, my tach needle started jumping around a couple of days ago. Once I get up to highway speeds and set the cruise, it stays steady at a little over 2K RPM, but when I'm driving or even idling it will jump around a bit.

Anyone have any ideas what would cause that?

Thanks!

 

Does the tach gauge match engine rpms, or just erratic reading on the tachometer?

The tachometer gets the signal from the ignition control module inside the distributor. The issue could be the ICM, wiring, the gauge cluster main board, or the tachometer. I'd start with the simplest item and check for any obvious corrosion/loose connectors on the ICM by removing the distributor cap and maybe the rotor.

 

Best I can describe it is akin to a wobbly speedometer needle in my older vehicles that needed a new speedometer cable or needed the cable lubed. The needle jumps up and down with the actual engine RPM's normally being around the mid point.

At idle it will jump up to around 1K.

At 1K it will drop to 0 and then jump up to 2K.