My /6 is a gas pig when it's cold outside. Why?

No definitely a cold blooded animal. My super six Volare wouldn't get **** for mileage in the winter and the gauge took forever to move. I would routinely warm it up for 10-15 minutes before driving to school. If I tried to drive it without a warmup it would choke and sputter and sometimes even die at every stop sign in town. What a pain. I usually got about 17 mpg in the winter. If I warmed it up though I never had a problem the whole day. I also credit the bad mileage though to my tune. I was 17... it didn't have a tune. Lol