What causes the rpm's to go up and down at idle? When I pull up to a light and take it out of gear the rpm's drop and then come way up to 1500 or 2000 or so and then go back down to around 500 and sometimes it dies but most of the time it straightens itself out. I have had a couple of foxes do this but never figured it out. The car runs pretty rich too, but I don't know if that would do it. Maybe MAF or o2 sensors? What do you guys think? Thanks for any input.