One problem related to speed control cable has been reported for the 1998 Audi A4. The most recently reported issues are listed below.
1998 Audi A4 2. 8 - driving along highway, in 7 degree temp, car started accelerating ( feels like it is driving itself) even after foot was removed from pedal and full force had to be applied to brake to stop the car at which point it went into high rev and engine was immediately turned off. Mechanic could find nothing wrong. This car also had 2 similar incident (once when new) and once a number of years ago. After much back and forth with Audi, they took the car in, and said they could find nothing wrong. As a precaution I had the cruise control disconnected and the throttle body cable replaced so felt the car was safe. (all at my expense).