3.2 idle problem

[Ned nyna 11]

Guys,
I set the throttle to be sure it was closing. Next I verified the operation of the air flow flap. I set the idle speed controller switch so it switches at idle and switches again when off idle.
All this work and the idle now cycles at a once per second or so frequency between 1000 and about 1200 rpm. Most aggravating.
Next, I swapped out the idle controller with the other one, I like having spares. No change in the cycling.
Finally I blanked off the controller hose, and left all the electrical connections intact the idle is now what it should be. The cycling is gone. Speed is adjustable with the little bypass screw.
One other clue is that with the system as designed and the cycling idle, it was difficult to get a smooth transition from closed throttle. There was a little jerk as though it was getting too much gas. With the idle hose blanked off, throttle take up is fine, the little jerk has gone away.
Am going to be happy with the present set up for a while but would truly like to know what the problem is.
Ned Monaghan