2002 Chevy Silverado problem with my pick-up when it's cold

I have a Chevy Silverado 1500. It doesn't idle well when the temp outside is cold (like below 25 degrees of so). Even when the engine is warm, it still will idle poorly. Not so bad that it stalls, but close. It is all right when i'm actually driving it instead of idling. It does not do this when the weather is warm - only when it's cold outside. Any advice would help. Thanks.