Wants to stall during cold start-up

I have a '90 LeSabre with the 3.8L and it normally runs great. When I first start it up during cold start-up and then within 10 seconds or so put it into gear the r.p.m.'s drop and it "hunts" (computer trying to set highet r.p.m.'s) and sometimes stalls. I removed and cleaned the idle air control valve yesterday which was full of carbon, and the throttle plate in the throttle control body is also clean. Maybe the idc is faulty? Anyway of checking without substituting with a known good valve?

Never does this once it warms up, and only when switching from Park to Drive, or Park to reverse when sitting overnight (cold engine). Any ideas? Thanks.