don't turn that screw...threxx is right. it's the base idle screw, which is calibrated at the factory and doesn't need to be changed. the idle is electronically controlled by the ECM. if it is idling high, there is a reason for it somewhere. could be as simple as a bad thermostat for the engine temp ECM reading...maybe MAP sensor...

mine idles at 700-750 once warmed up...i have a 5-speed so i can't give D4 rpms...

changing that screw will not confuse the ECM, since the ECM has an input for tach speed. what it will do is prevent the ECM from having a full range of adjustment control over your idle speed. the car comes with that screw set to a median point, at which point the ECM changes that point up and down depending on atmosphere, temperature, and fuel.