Hmm I have a similar problem (R33 gtst)
Start the car, works fine, cold, idles at 1100 or so. Warm, will idle at 900 rpm no worries. However, if im crawling at an intersection or in heavy traffic, if I move forward, then to stop just put the clutch in and stop, the revs drop not to idle like they should but to very low, like 200-500 rpm, the engine shudders abit, then jumps back upto 900rpm idle and is fine. But it keeps threatning to stall everytime it does this?