What would cause the engine to idle rough after starting then runs smooth?

What is your question?

Once the truck is started and starts to warm up it will gradually start to idle better. No engine lights come on and once its started and warmed up it runs fine. All ready changed plugs. Wondering if its a bad IAT sensor or something to do with the emissions. Couple times it wouldn't start back up after driving for short while. Any ideas as to what could be the problem?