Does it stall immediately after you start or is there time involved?
Does it run when you are idling but stall when you give it gas? If it
takes a while, does it stall when you turn on lights and AC?
A good mechnanic with the right equipment should be able to tell which
(knock or crank) sensor is bad -- it is not by any chance the same guy
that replaced the distributor, is it?

Sorry about the questions, but it really could be a lot of things by
your description.

Remco