Australian Car Repair Issues? Ask an Auto Mechanic for Answers ASAP
I have seen many Vivas with your described issue.
Having worked for Holden for many years, I have fixed lots that others can't fix, they get towed in from other workshops.
A good Holden tech will fix your problem.
Could be a combination of throttle body base idle reset, IAC learn procedure, and a upper cylinder clean.
Not many realize the importance or IAC steps open at idle.
If you don't have the inlet manifold rattle, then your ECM has the latest software.
Hope this may be a start for you.