This may sound strange but our R33 (sII) was idling at 1500rpm and we couldnt figure out why, firstly we got some carby cleaner as the throttle body was gummed up with carbon, then by chance we pulled out the idle stepper motor to find a piece of our impeller blade (we blew out the stock turbo 2 weeks earlier...) was not letting the plunger motor sit on its seat, so after we cleaned that out too and put her back together she was fine....
Hope u find out wats wrong with yours!!!!