My truck used to do that same thing. Had to bump throttle to get it to idle down.

Things to look for:

* Inspect the entire throttle linkage for wear…grooves, egged-out holes, etc. Something could be hanging. I recently added bushings and a ball linkage at the end…to smooth it out.

* If you leave too long of a “tag end” on the hand throttle cable, it can hang up on the top of the manifold in certain positions.

* Might need a slightly stronger throttle spring.

1951 3100