I've been seeing quite a few questions around the net about this, so I put together a quick video on how to do it.
I've attached a picture showing what the camera can't see.
I have an automatic, so I set mine at 850ish rpm (engine warm), in park, which put it at around 700-750 in D with the AC compressor running. This also negated my cold start stalling issue.
Hope this helps.