Fuel additive - Roger Jones
I had a persistent cool-running problem with the Audi 100 that I sold last year. It surged and stalled, sometimes in dangerous circumstances. None of the Audi main dealers who serviced it regularly over most of its 10-year life with me solved the problem, which was almost certainly attributable to coking up because of short-trip usage. I did solve it finally, with VAG's own fuel additive (part number G 001 700 03), which eliminated the problem entirely and gave me first-feather-touch-of the-key starting as well. I've sworn by it ever since and it's cheaper than the stuff you can get from accessories shops.
RE: Fuel additive - honestjohn
Dear Roger,

That's right. I use it too. But keep the bottle away from children and don't get any of the stuff on your hands.