What would cause the tach to jump around while driving ? Were talking milliseconds the tach will jump from 3500 to 7k then back to 3500: not usual tach progression. I have new clutch that ive babied for ever so I dont think that it is slippin. Speedo did it to once went from 120 to 110. I'm guessing i have electrical gremlin somewhere. Im getting around 14volts with car running on volt meter.

 

bump

 

Either the wire that goes from the coil i beleave or the tach its self. Try to find a friend that has a aftermaket tach and hook it up to your car and see if the problem is on the new tach also