I have a Enderly and Fast electronics on a 502 bbc. Believe me its not really made to run at near idle speeds. These are racing manifolds made to run at full throttle. I have similar problems. Your surging is cause by a lean condition. Some of these units like the Fast have a base program that you cant change, may not work for your application too many variables. Wont go into learning until it hits a certain engine temp. Manifolds don't have a plenum, so no idle air control. I have a small aluminum block with air brake hoses to each runner under the butterfly, doesn't really do a good job though. Lots of things to check to try to make it run better. Fuel pressure and a proper regulator is another. Do you have a return line to fuel tank? You have to sync all cylinders with a synchronizer and tweek each butterfly to get them flowing all the same, very time consuming. These are just some of the thing to do to try to get it running better.

KC