i got the same problem too.. it idle around 1500, but sometimes idle around 1000rpm. I notice when it idle around 1000, when I drive it give deeper sound from my muffler but when it idle high, the sound more rasp. when it cold it idle around 2000 and on cold winter sometime it idle up to 3000rpm
i also notice the engine running rich and lean almost all the time (my air/fuel ratio goes up and down, i thought it suppose to stay on same spot all the time)