I did this on my car this weekend. Background: engine stopped while cruising at low speed. It was possible to restart the engine after a while (cooled). This is typical behavior when the G28 sensor goes bad. You can find the exchange info here: http://www.audiv8.com/german/faq/faq_show.php?id=201
The connectors are somebit hard to reach. They are located directly under the vacuum clock for the auto cruise (under the left hand distributor)
It is often a good idea to change the other sensor as well.
Audi V8 3.6 1990 Gold metallic
Audi Ur-S4 2.2 1992 Black