It has been only a few days since I installed the new MAS. The check engine light has not reapeared, knock on wood, but it usually takes a while for it to come back on. If it does I will post here again. The car is running much smoother in the low RPM's and is more responsive so I think that did it.

I am not aware of having to reset the fuel trim other than turning the Check Engine Light off by disconnecting the battery or OBDII port.

What is a good way to check for a vacuum leak? Those lines run to multiple places and seem to be controlled/vent thru the electrical gizmo/manifold on the front of the engine (near the water temp sensor) on the C230.