I have recently brought an A3 1.8T 1998 with very high miles but full Main dealer history.
After only a week i noticed poor and erratic idle together with general poor response.
A couple of days ago it got to the point where it would just hunt then die all the time.
Last night i removed the throttle body,Cleaned it thoroughly,including sensor in inlet manifold,all was fairly well coaked.
Car now idles perfect,no hunting at all.Runs smooth.
Took all of about an hour.

Well happy.