had loads of issues with mine not idling - first thing i would do is get it on VAGCOM see what errors come up. i would suspect the breather pipe from the inlet manifold to the ecu would be the culprit. (usually shows as inlet manifold pressure sensor on vagcom).
failing that coolant temperature sensor?? isv does tend to go - clean it with petrol and a little redex, making sure you dont get the electrics wet. if possible see if you can swap for one you know is working!!
Failing that there are hundreds of threads on hear if you use the 'search box' work your way through the list till its sorted.
