Did you ever get this fixed bteoh? As others have pointed out, a rattling PCV is what you want, so that isn't your problem. It's a one way valve and the rattle is a ball bearing. When I originally took mine off, if I shook it, I could feel the ball bearing sticking at the extremes of travel. Carby cleaner through it cleaned out the gunk. With a good one, blowing through it one way it will flow, sucking through the same aperture, it should seal closed.

My original idle issues were totally different to your hunting around 1000 rpm and near stall. Mine was varying up and down completely randomly from near stall up to anywhere around 2,500 rpm.

I'll edit the original post as it looks to me increasingly like I either got lucky, or it was the PCV valve. My problems have not arisen since the original post.