will start but won't idle until engine warms up

I have a 99 Explorer 4.0 SOHC that will only start when I pump the gas pedal. The problem reminds me of trying to start tractor or motorcycle without using the choke. What I mean is that the engine won't idle and will stall unless you stay on the gas. Once the engine is warm however, it runs perfectly. It also doesn't seem to have this problem in warm weather (75+degrees). Has anyone had any similar experience?

Possibly the Idle Speed motor. Or maybe the engine coolant temperature sensor.

Thanks for the quick response, I'll give it a look.