DonnaC,
I had that exact same thing happen with a 201. Sews fine, stop to do something, push on the controller it won't go. Touch the hand wheel and zoom away it went.
What I found out was that the commutator, brushes and their tubes was contaminated with oil. I carefully removed the brushes and cleaned them and the springs and caps with denatured alcohol, then used a q-tip with the alcohol to clean the commutator and brush tubes.
End of problem the machine works fine now.
Joe