I was looking through some threads elsewhere and noticed a lot of people mention that after their cars have been sitting for awhile (overnight) on startup their cars will go up to about 1200 rpms and be a bit louder than normal (like something else has turned on in the engine). Slowly the rpms drop down to about 850-900 (regular idle) after about 30 seconds and the noise stops (or whatever is making the noise, shuts off). I heard it's something to do with air being pumped through to the cat converter for emission control purposes or something? Can anyone explain what exactly the car is doing when it does this at startup? I'm curious.