I remember a while back when sorting some idle problems on my RB25/30 DET R33 with PFC, that at a certain very minute openning of the throttle, just passed closed, I could induce this same hunting condition repeatably. I also came to the conclusion that the idle control algorithm of the PFC was inferior to the standard ECU, but I managed to fix it eventually after much hair pulling.
What engine are you running ....RB25,26...I cant really see clearly from your avatar? The 26 has a throttle switch as well as a TPS, wheras the 25 only has the TPS. I assume you have the correct PFC for your engine? What AFM are you using? Have you removed the screens etc?