I have 98 civic with a 99 b18b1 and hondata s100. I am using the civic's ac. Just recently I have been having idle issues with the ac on. RPMs will drop to 300 at a stop and the kick back up the 800. If I try to hold rpms at 2000 with the ac on the rpms will go up to 2500 then down to 1500 on its own with me holding the throttle steady. AC works great and high low side pressures are perfect. I have had the swap done for a year now and this just started happening. Any ideas on what it could be? Need some input until I can gett the car to my tuner so he can plug in and data stream from the hondata to see whats happening.

seems like the idle is surging...i would check the IACV and check coolant to see if there are a lot of bubbles in it