It is best to remove it. I use carb cleaner and a toothbrush. Scrub it clean, making sure the edges of the butterfly are clean. Try to avoid holding the throttle body in position that allows carb cleaner to run down into the end that contains the electronics. Be sure that the very small openings are clear. Carefully remove the bottom portion that contains the adjusting screw and clean that as well (not just the plastic piece, but remove the hex head screws and clean the interior).

If someone in the cars past has adjusted the idle with anything other than the plastic knob on the throttle body you may get a very high idle after the cleaning. If so come back and post for information on the base idle setting- available in the Bentley manual (you do have one of these slated for your library, right??)

Randy