One problem related to car throttle sticking has been reported for the 1998 Audi A4. The most recently reported issues are listed below.
Throttle sticking on acceleration in sub-zero driving temperatures. Brakes enabled me to stop car and shut off engine. If I took my foot off the brake, the car re-accelerated to the stuck position. Once the engine was shut off, engine heat evidently melted the ice and idle speed returned to normal. Have spoke to other Audi owners and they have experienced similar stuck throttle problems in sub-zero driving temperatures. Independent Audi repairmen have suggested the problem is caused because there is no source of heat (exhaust hose routing or engine cooling routing) near the throttle plate and there is no fix or repair to this design problem. If a crash occurs, the engine heat melts the ice buildup before a cause of accident can be determined. When I contacted an Audi dealership to ask if this is a problem with others and to get repair advice, they were unaware of this problem type and just said to be very careful driving. I also contacted Audi customer service to file a report and they also said they are unaware of this being a problem but did give me a case number (881108347). It is -9 degrees today and -18 is forecast tonight. I am afraid to drive this car in sub-zero temperatures. Next time I might not be on a back country road when the throttle sticks.