Bad idle, from the cold???

[Aslet]

I just replaced my intake manifold gaskets, vacuum lines, and had the injectors cleaned. I go out for a test drive, the car starts fine and even when I pull out of the garage keeps a good idle. After driving 10 miles or so, letting the car warm, then driving it hard, pull back to the garage and there is a bad hunting idle (800-1200)?!?! Could it be that the car is warm and since it was being run hard, the cold air is messing with the air/fuel mixture? It has done this twice now, the second time it stabilized on its own after about a minute... Is she just mad for being out in the real cold weather? (around 5 degrees before wind chill...)

Any thoughts?

THANKS!