I know what you're talking about, but that's not what I'm describing. With the IAC unhooked, the car runs for a while, and putting my hand in air tube (without airbox or MAF) I feel no vacuum or moving air, but motor's still running fine. After 30 seconds or so, I hear the RPMs settle and motor dies right about the time I hear the sound of intake start to pull air through TB (a rushing air sound). This may be normal operation for all I know, but at that point, motor's dying . . . and it's starting to **** me off.
I've decided I'll check for continuity, voltage, ground, and short if needed, between the two CKP wires at PCM and at sensor if needed, and also recheck fuel pressure at rail during the unhooked-IAC 3o second run. I will also likely get a motorcraft IAC just to fully rule that out. After that, I'm saving up beans for a trip to Atlanta . . . I have family with a trailer and I think my '15 F-150 3.5 EB needs to flex a bit.