A 35 will not idle down if the throttle rod is not set correctly where it connects to the governor linkage. There is also a spring on the governor linkage, have you checked to see if the spring is there, broken or if it connected correctly.
I had the same problem you are describing after reinstalling the cylinder head on my MF 150. If you are missing any of the parts, chances are I have them. We just finished parting out a MF 50 and To-35.