Hi reading other posts the judder sounds like the maf or the ecu, the maf can be cleaned and the ecu reset by disconnecting the battery for 15 mins. But if you have an alarm you may have to reset that as well, also know your radio code.
I bought my daughter an 8v Mk3 gti and this has the same problem, I will attempt to fix this weekend.
Also I bought some new ign leads and it was like Blackpool illuminations sparks everywhere, so they will try and get some Bosch for me today.