Put in park or neutral and the engine idle drops

[crazy.vr]

Gday, lately my VR V6 has this engine idle problem. The car drives fine, idles fine but when I put it in park or neutral from being in drive or reverse, the engine idle drops to 300-400rpm and slowly goes back to normal after about 3 seconds. Any ideas? Thanks.

[aceventura]

IAC valve would be my guess, if you haven't done already, might want to give it a clean.