Fast idle in extreme cold

When it is very cold out (-20 C or colder), my truck will start okay but will not fast idle long enough to remain running. It stalls after about thirty seconds. This problem is new this winter. I can manually rev the engine up for a minute or two and then it will be okay. The check engine light does not come on. My engine does not have an idle air control valve.
What is the most likely culprit? A sensor of some sort? The computer?
The truck runs perfectly fine otherwise.