Need some info for the tach. I drove home from work over lunch and when I started my car to go back I noticed the tach didn't come up. When I revved the engine it started jumping sporadically until it pegs up against the clock and stays there until I shut the car off. Then it does the same thing until it goes back to zero and repeats every time I turn the car on/off. I have a 97 quattro with the 12v 2.8.

Main question is if the tach is controlled by the pcm or if it goes off a sensor. I'm a newly graduated auto tech but I haven't worked on Audi's before and I have very little time away from work. On top of that the dealership I work at does not have acces to alldata or mitchel (Ford dealership so all they have is Ford scan tools)

 

Connect an OBII scanner and see what it says for RPM, that way you could rule out whether it's a sensor/wiring or the gauge itself.