Yesterday, my tack started jumping around. It is as if the signal just cuts out (short perhaps). Most frequently at idle. It will be idling fine at about 600 and then the tach will drop to 100. The engine continues to idle smoothly. Is there a usual suspect here? Ground perhaps. Never tinkered with the instrument cluster - don't even know off hand how to get into it to check. Where do I start?

Any help would be greatly appreciated.

It's an auto, so I don't need it for shifting pruposes, but it would be nice to not have it jumping.


Thanks,
Sam