In the Usenet Audi newsgroup there are scattered comments about the being a problem with carbon build-up on valves in the 5-valve-per-cylinder engines and that Audi doesn't have a solution to it. This may only be a false rumor, or a problem that affects only a few cars, or a result of using the wrong gasoline, or something similar. Could owners with a lot of mileage comment on whether they have had an engine problem?