Bouncy tach

[suprdave09]

My tachometer is real bouncy on acceleration and every once in a while at idle. It's like it is getting stuck every 400 rpms then grabs. Started off only doing it once in a while now it does it all the time. My datalogger and s-afc read solid rpms and dont bounce. any ideas on what this could be.

car is a 90 AWD.

 

[DSM90AWD]

My tachometer is real bouncy on acceleration and every once in a while at idle. It's like it is getting stuck every 400 rpms then grabs. Started off only doing it once in a while now it does it all the time. My datalogger and s-afc read solid rpms and dont bounce. any ideas on what this could be.

car is a 90 AWD.

The 1990 tachs feed off the tach driver on the coil pack, so either the connection is bad, the coil pack is bad or the tach itself is bad.

 

[suprdave09]

Its only when there is 0% throttle on deceleration. Just was messing around with it, any ideas?