I have a MY10 N52K engine that i don't drive a lot (17K Kilometers) and it does the same, although it does not drops as low as yours.
On the first 2 seconds of cold starts it usally has unstable idling between 1000RPM - 800RPM . . . just the first 2 seconds after that it idles fine.
Last edited by UltimateDriving; 12-12-2012 at 02:02 AM.