When outside temps are low (under 45F, I would say), the engine in this car stumbles/hesitates before it is fully warmed up when I am pulling away from a stop (e.g. at a level intersection -- but same on a slope). In the summer, with higher air temps, it doesn't do that. I'd appreciate suggested explanations.

The engine starts at any temperature at the first try.

 

My guess is that you have a bad idle control valve.