Maurice! How Are Things In The North?
Fuel filter (i.e. bad gas lines) weren't the cause, but I kept the filter in to protect the fuel distributor - I think it's an excellent idea. Soon I will pull it, replace it with an identical one, cut it open, and see what I find inside. This should give me an excellent analysis of the internal conditions of the fuel line. Judging but the shape of other things on this car, I suspect they are in good shape, though.
No, it's a combination of things. Now it's only rough after shutting it down and letting it sit for a few minutes. When you start it cold, it's fine, when it's all warmed up, it's great. So it's either carbon or one of them chips and/or a related sensor. But the car has been behaving so well that I have basically forgotten about the issue.
I did have to replace a leaking EHA control valve.
In terms of the the other responses - I am afraid there still may be a problem, after having driven it 12 miles today. I figured out how to remove the back cover of the fuel tank - the screws on the bottom are hidden by the felt liner. I am going to look over the connection to the fuel filler spout very carefully.
1989 560 SEL (black/black)
2001 Audi TT Roadster (silver/grey)