Did you resolve this issue? I bought one of these for my daughter, did the cam belt and other maintenance items and have been having exactly the same issues.
We are in Wellington and she is up in Palmerston North at Massey. I am off up there this weekend with a replacement throttle body to see if that cures the problem.
This has to be the most unreliable car I have ever owned and the most difficult to diagnose. My local auto electrician can't find anything wrong with it and every time we take it to him it runs fine. Next day..... Last time I was there he had another one with the same problem. The bugger is that other than this it is a great little car for her.
Cheers
Martin