How to Troubleshoot the Cruise Control in a 1999 Audi A4

1. Locate the fuse panel beneath the steering wheel. Lift up the fuse panel's release lever, and pull down on the fuse panel.
2. Inspect the fuses of the cruise control and brake lights. A diagram under the fuse-panel lid will shows where these fuses are located. The cruise control system malfunctions if the brake lights are damaged, or if either fuse is damaged or burnt.
3. Turn the ignition key, and inspect the vacuum lines of the brake booster and intake. The cruise control system might be malfunctioning because of a vacuum leak. If the car is idling roughly -- or if the engine bay is making a sucking sound while running -- a vacuum leak is often the problem.
4. Inspect the throttle cable;. A damaged or corroded cable will prevent the cruise control from accurately controlling your Audi's throttle.
5. Turn off the engine, and remove the negative cable of your A4's battery. Detach the retaining nut on the negative cable, and carefully take the cable off its clamp.
6. Inspect the combination stalk and cruise control module. These components are rarely damaged, but they might be the source of a problem. Use a screwdriver to detach the screws that keep the steering wheel's column cover in place; remove the cover of the steering column with your hands. Pull out the plug from the cruise control switch, and detach the screws that fasten the cruise control stalk to the steering column. Replace the stalk with a new one.