Setting up a choke servo
I'm sorry to say that I don't see a way to make the pot work only at idle. I've tried several different ways and depending on where the pot is, if you mix it in with the throttle, no matter what, the throttle stick will move the aux channel. You can just plug it into the aux channel and use the pot, but in order to make it limited with the throttle stick, it will need to use a switch.