Sorry to bring up such an old thread, but the issue didn't seem to be resolved above and when i experienced the same issue this post kept popping up in my Google searches.
My 2003 Bora 4motion had the exact same problem with the haldex unit locking up on tight turns and "hopping". I went and saw Seb at Euro Auto tech in Girraween and he replaced my haldex controller with one from another car with low kms. This completely resolved the issue immediately.
I suggest finding a second hand unit and getting it installed. Mine cost me about $200 including install.
Hope this helps!
Sam Brennan
2003 Bora 4motion - Mk5 R32 Swapped
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