I appear to have exactly the same problem. Stopped off on the way home from work and when I started the engine again the revs rose to just over 2k rpm for about a second before it settled to idle. Pulling away I noticed a lack of power and general sluggishness which I assume is limp mode. No warning lights or smoke under acceleration.
Did you need to do a VAG-COM scan to locate the boost solenoid problem, and is it easy to get to? I have no idea where this is in the engine.
Car is a '98 1.9TDi quattro AFN engine with 183k miles.