dodge neon troubles HELP!

I have a 95 dodge neon sport coupe DOHC...its great but i have a few performance issues. Whenever I have the fan set on front windsheid defroster the car will rev up and down while idling. Also when I am coasting to a stop with the clutch pushed in, it will idle down to maybe 2000 and not idle all the way down to 1000 until I am completly stopped...whats up with that?? It also will sputter every once in a while while driving it (very minor though). And after it has been drivin for awhile a high pitched humm comes from the ecu. Any help would be great!!! Another thing is there is a knocking coming from the rear right side and its not the strut.