I have a 2003 A6 with a 4.2 and the temp guage is either resting all the way to the left or in the middle where it should be (after normal driving). There doesn't seem to be any reason as to when it chooses to work. Is there a sending unit for this I could track down and maybe make sure the wires are tight/replace the sensor?

 

It was a simple temp sender. Easy to replace, just when you're ordering parts don't kid yourself into thinking the clip will be re-usable, it's plastic and break requiring you to drive to an audi dealership at an inopportune time.