Another possibility may be the THERMAC system's vacuum motor; if it is not the main cause of the problem it could be part of it. The snorkel coming out of the air filter should have a vacuum diaphragm and it will actuate when it is cold (so long as the temp sensor in the THERMAC assembly is good).
This heats the intake air because some/most is taken from air around the exhaust. Lastly, there should be a tube going from the bottom of that snorkel to a metal piece near the engine's exhaust manifold.
This page may be of assistance:
http://www.73-87.com/7387garage/drivetrain/thermac.htm
My 85 305ci Caprice has issues in the cold because the temp sensor does not work right (costs too much for me to replace currently). It will stall and be sluggish until about 3-5 mins of warming up on cold days.