Thanks for the info and explanation. I think I was able to isolate the problem. I have access to another c280 and switched out the AMM (air mass meter). After the first trip, the other c280 came up with the CE light and the idle began to hunt. I don't know what the code is but the results are pretty obvious.
In addition, I noticed a very distinct behavior where the idle would not hunt with the AIR CONDITIONING on (steady as rock) but will hunt immediately and pretty dramatically when it is turned off. Does this indicate anything specific? I'd like to know how this system works. Does it indicate any other problem part? Thanks.