How do you fix high idle problem on a 89 240sx?

If your idle was fine and then just became high, don't adjust the idle control screw. Your problem would be indicative of another issue. Perhaps a vacuum leak. turn the idle control screw to the left ... no neither of those.....your are getting air that is accounted for by the mass air flow sensor....there for its either a) throttle plate not closing or b) idle air controller stuck open.