Well, I hear you on that, CB. However, first things first.

I did, as mentioned earlier, find that the O2 sensor had been left unplugged. When I connected that, the rough idle and stumble at low speeds went away. But it still would not idle at low RPM when partially warmed up.

Yesterday I pressure tested the intercooler system from the turbo to the throttle body. Lo and behold, a big old vacuum leak in this hose running from the intercooler pipe at the TB to an apparent servo valve near the passenger side fender. This hose had looked like new, but had a big crack on the bottom where I couldn't see, by the nipple leading to the IC pipe. Trimmed off the last 2" and then was able to maintain pressure from the turbo to the TB. Just test drove it this AM - about 20 degrees out. No stall at idle through the warmup cycle. Idling high (as expected since I had the throttle adjusted high to keep it running previously.

Will adjust the base idle when it warms up a bit outside. What is that hose/servo valve anyway?