Geo55

So I took my car to get the windshield replaced and noticed that the tach never moves more than to the 1000 rpm mark for example, At 55 mph the tach reads 750 rpm and at 80 mph the tach reads 1000 rpm. otherwise the car runs fine and starts fine. The Tach does move slightly when I turn it over to start the engine. Any ideas what may cause this phenomenon? 1987 S4.

Geo55

Calling Dr. Bob, Mr. Merlin, or any one of the masters, please help.