IM bolt removal - 83 5kt

[Tex Terry, II]

Of the four bolts holding the sandwiched throttle butterfly, in between the
two parts of the IM, three of them came out okay. These are allen head
brass bolts.  The fourth bolt started to turn loose annd then started to
get harder to turn.  I stopped for fear of  breaking the bolt off, or
possibly stripping the aluminum threads in the IM.  Any suggestions on how
to proceed?  I was taking the section apart, instead of taking off the
whole IM, so that I could try to find the hose/bolt plug that went in from
the cold start valve hole.  Thanks, Tex.