Man, this thread is all over the place! Spark plugs, Air Injection, Transmission adaptation, etc. The answer probably isn't too hard to find, as long as you look in the right place. I realize not everyone has SDS at their disposal, but here's what I'd do if I was working on the car.

It sounds as though the throttle actuator could be the problem. The first thing I'd do would be to make sure the fuel trim values are within specification. This is a reliable, fast way to eliminate the possibility of a lean/rich condition causing the problem. If that checks out good, I'd activate the throttle actuator using SDS. It's a simple test, done with the engine at operating temperature/idle speed. The throttle is slowly closed, lowering the idle in small steps. Then I'd see if I was able to open the throttle up again. Sometimes the actuator simply isn't strong enough to overcome the throttle return spring. I see lots of this on higher mileage M111's. The result is a fluctuating idle because the actuator doesn't react quickly enough to stabilize it.