Jumpy/Inconsistent Tach
 

Background:

90 Chassis
DIY MS3X
02 VVT Motor

So I've had the car up and running on the MS3X and VVT motor for about 2 months now and for the most part things are fine. Two mornings ago, my tach started jumping and bouncing around, it usually stays between 4 and 5k. It will be normal on startup but will go inconsistent within a minute or so. When I get to about 4500rpm the tach signal is synchronized again, all the way to redline and will be inconsistent as soon as they fall below that same threshold.

The car ran normal and TS displayed the correct rpm so my first thought was wiring. I checked the grounds and my breakout box and everything seemed fine. This afternoon, the car would be idling and the tach would be synched, then it would go rich and die unless I kept it alive with throttle. I can post a data log as soon as I get home. Any other areas I should check?