So many people seem to have a bad idle problem, i just thought i'd post this snippet that was extracted out of a vw mechanic.
If you have replaced everything and you still have rubbish idling check Fuse 18 (or 17). (This works for 16v at least just in case it model related).
Apparently, this fuse blows, you take it to the garage - they charge you 300 quid to "fix" your problem.
Justin