2000 B4000 Mazda 4.0 Liter. In cold weather truck will start but idles at 2000 RPM, when placed in reverse or drive everything is fine. Drives and accelerates as it should. Only on cold mornings, temp approx 32F to 20F. Is it the idle control regulator?

 

I'd check the coolant sensor. I'm not sure of which obd it is on your truck but it sounds like a cold start circuit isn't disengaging