I could be wrong, but I believe that changing the coolant temp sensor and mass air sensor was a waste of money. The water pump was changed, then the problem started. It simply makes no sense that either of these sensors are involved.
Think about what Arthur said...vacuum lines, etc. I believe that Benzmac mentioned the large vacuum line that runs underneath the intake manifold in another post.
I'd bet a couple of bucks that your mechanic knocked something loose when he pulled the pump or something related to this task.