How long since a tune-up? Any applicable mil codes? You should be able to check mil codes, yourself. Use a gage and check for correct fuel pressure. Also, see if pressure will hold for a bit, with everything off.
Block off the mouth of throttle body, engine idling. Does that have any effect on the idle? It should kill the engine. If idle is still high, you got false air getting in there from somewhere. Vacuum leak?