When i bought the car a couple weeks ago, the tach hovered around 4k at idle, and would always return to it at idle. When driving the tach would immediately go to 7k+ plus and stay there permanently. I recently changed the spark plugs and wires, one of the spark plug wires was corroded badly enough to come apart when i removed the wire, part of it was melted on the spark plug...

when i fixed the plugs and wires and i fired it up the tach went down to absolute zero, and started dancing... kinda got my hopes up that maybe the tach would/could be an easy fix...

is there a sensor or sending unit i could fix/change or is my guage shot all to hell?