I had the same problem show up when it got s-o-o-o-o cold here. Checked/cleaned IAC, IAT sensor, ECT sensor EGR solenoid and valve -still problem. Finally bit the bullet and removed upper intake manifold -- the gasket was completely crap! Replaced Gasket(s) -$22 each from dealer here in Canada, and purrs like a kitten again. Try squirting a LITTLE wd40 or similar around UIM/LIM gasket area. If they're leaking, it may temporarily seal them up and smooth out idle. Only temp though, replace em ASAP. Good Luck!
