Can tach be disconnectd?

["hootspa@zzapp.org" <hootspa@zzapp.org>]

I've got an 89 Audi 100 wagon w/automatic trans. The tach started acting
up and the needle is flying all over the place.

1. Don't really need a tach on an automatic trans car.  Could I just
disconnect it without it screwing up the input to the fuel injection
computer (does it have RPM's as in input??)?

2. How do I trouble shoot it? Is it more likely to be the tach or the
sending unit?

- hootspa