What's the hottest ambient temperatures you've driven the car at? Have you noticed that it idles faster when it is colder? I notice that on mine, the idle is completely dependent on engine temperature. From cold starts, the engine on mine idles about 1500rpm for the first minute, then drops to around 1000 for several minutes. When it gets completely warmed up though, it idles at about 750-800 (more with A/C on). I imagine there are many variables at play determining this idle speed/mixture. Also, indicated fuel consumption at idle can vary as much as 4 to 1 (determined by instant mileage gauge at slow speeds), suggesting that the fuel mixture as well as the RPM can vary. When completely warm though, the engine consumes very little according to the display -- about 0.1 gallons/hour.