Surging idle 01 MDX

Have an 01 MDX with 72,000 miles coming in to the shop this week with a surging idle. Once closed loop is achieved, idle surges from around 500 RPM to 1200 RPM quite rapidly, and most of the time, but not always. When off idle and driving, it performs fine. O2 sensors flip flop rich to lean with the surge. TPS reads about 9% at idle. P0505 is set, (Idle Control System Malfunction, no kiddin'), and the SES light is on. Any ideas?

could be a vacuum leak and or a iacv=idle air control valve