[s5uewf]

I would plug the actual idle air circuit to eliminate the possibility air is leaking past the idle air control motor line. Then I would set AFR and idle speed at normal operating temp and see if it is stable then or if it still creeps up.

If you suspect an air leak and it is manifesting itself at idle, I would suspect your AFR's would go lean at idle as unplanned for/unmapped air is entering the system and leaning the mixture.

I have a sort of similar situation with my Bosch 2 wire IAC - if I plug that loop off and set idle and AFR's perfectly, I get a nice idle and stable AFR's - but I lose the advantage of a high idle/choke type effect. If I connect the IAC circuit and activate the IAC motor, my idle goes higher and my AFR's go leaner because some air leaks past the IAC motor even when it is closed. I need to compensate for this by adding fuel and lowering my idle stop and then I can achieve a stable idle and still get good cold start, etc.

I would say the idle air control is the most troublesome aspect of my entire EFI system. And it is not "really" needed ...