Why might it be doing this? Could it be my AIT sensor? What?

 

warm up mode.

later
tim

 

So it's just a normal thing? My friends 91 RS doesn't do it as bad as mine.

 

mine does the same thing...always has...itll calm down once it warms up some

 

open loop

 

Not quite, it's a warm up mode. Open loop has to do with the Oxygen sensor's temperature(and it will open loop kicks in when you approach WOT), I don't think open/closed loop effects idle that much.

 

I just wanted to claify something here. Open loop happens when you first start your engine and lasts until it reaches operating temperature and the O2 sensor is hot enough. When in open loop the ECM doesn't moniter the O2 sensor and calculates how much fuel to put i the engine from tables in it's memory. An engine also goes into open loop if an error code is tripped. This is also known as limp home mode. It is used to that the engine continues to run even if a sensor gets messed and returns a messed up reading that would normall cause the engine not to run. Closed loop is how the engine normall runs when it is warmed up. In closed loop the ECM monitors the O2 sensor and tries it's best to keep emissions low as opposed to open loop where the ECM just wants to warm the engine up or keep it running. At WOT the engine also ignores the O2 sensor and richens up the mixture greatly for more power

 

very common. Don't worry about it. Mine does it at 1600 RPM.