Hi David,
I'd seen that from
this thread - However that assumes you know how to do an output test!!!
I did find
this PDF which describes how, albeit on a 40v A8 rather than an S8. However that also mentions various VAG gear that i'm guessing VAG-COM replaces to some extent.
I have however found
this rather useful thread with lots of pictures and diagrams and have gotten my head arround what it is and what it does.
Popping the bonnet and grabbing a friend, I've just checked if the bellows are doing their stuff. They are fully closed when just idle and playing with the loud pedal round 5-6k rpm they release, which seems to be what they are supposed to do. I did have a fiddle with the cables and sensors arround that area, unplugging and replugging as well. Clearing the code and it seems to have gone, so i'll see what happens on a ride out later.
Reading through things, it seems you get a bit more torque or pepp from the engine at low and high revs, depending on the pathways. Neither of which should cause any major show stopping problems!
Lee