Digital Cluster RPM's erratic and jumpy
 

I have a 91 S10 blazer with a 4.3L TBI. It has a 700R4 and a NP231 if that will be helpful at all. Fuel pump was recently changed, Distributor assembly is also new. AND the heads were rebuilt.

When i am at a stop light or at a low idle my tachometer starts going crazy. Sometimes the motor will even hiccup as if it wanted to backfire. When i accelerate, the RPM's smooth out and it acts normal with accurate readings as far as I can tell. I changed the MAP sensor but did not fix it (I had one handy). The other idea I had was that it could possibly be the TPS? Since it only does this at a certain throttle position that would be my next guess. I have a link to a video on YouTube so that you can see what I am talking about. Any assistance with troubleshooting this annoyance would be most appreciated.

Solved. I seemed to have stumbled upon my solution. The distributor was changed out about a year ago. A screw has become loosened inside the distributor that was responsible for maintaining the gap clearance between the reluctor and magnet sensor. Essentially the reluctor was spinning around and smacking the magnet. I re-gapped and cleaned up the guts of the distributor. Changed cap and rotor. Good as new.