Well after a little searching i see others are haveing the same problem with the tach jumping all over the place out of nowhere. But on mine i notice that if i take my foot off the gas completely it goes back to normal. Then when i go back on the gas it goes nutty again. Which leads me to think that the sending wire in the engine compartment is badly connected. Which wire is it off the distributer?

what rig do you drive? A nissan i know that, but is it a frontier, or a pathfinder, what year.. ect. this might help get a reply.

I have only seen this problem when you have a fireworks display inside your rotor. Not that there can't be another problem, just what i've seen.

So sorry..... '95 Pathfinder w/v6, auto tranny, 4x4.