It will be your tps "throttle position sensor" it sits on the back of your throttle body.
I would replace it $25 from a wreckers or $90 from holden. If you buy some tools from kmart you can change it yourself. If you rev the engine it will slowly idle back down right . If yes its is the tps. Hope this helps.
Ps check the map sensor hose too make sure there is no cracks etc or broken parts its at the back of the engine too . near the firewall. Look it up on Google. Good luck with it if you still have not fixed it from feb this year. Maybe it will help others.