It's not running rich, it's burning oil.

Either the valve stem seals are bad and it's burning the small amount of oil that leaks past the seals and into the cylinders when it sits or, more likely, it's burning a small amount of oil all the time but you only get visible, odoriferous emissions when the cats are cold. When they get up to operating temp, they do their job and the light scattering PM/VOC we like to call smoke never makes it out of the tailpipe...