The idling issues which seem to be a problem for a lot of people seemed to come and go for me. I'd scrub the throttle body, clean the MAF sensor and it would go away... For a while. The Lambda sensor seems ok, it seems to cycle between 0 and 0.6v regularly so it's not dead at least.
This time though none of these seemed to work, so I seen someone mention something about the battery terminals. The voltage was pretty stable at 13.9v and a good 12v when off, so I didn't think it was that.
Anyway, got nothing to loose so I unhooked it anyway and took some sandpaper to the battery terminals and also the inside of the connectors. No obvious corrosion that I could see, but it did seem to have an effect. I don't know if it was related to resetting the ECU (idle revs jumped to 2k until the ECU re-learned) or the connections themselves but it's idling an awful lot better now. It's still not perfect, but at least it doesn't sound like it's about to cut out anymore.
So if you have an idling problem, it's well worth trying this before investing in an expensive sensor replacement.