Re: 83 johnson 75 hp
The major problem that the mechanic found on mine was that when the fast start/high idle lever on the remote was pushed down, the cable didn't retract properly on the engine, hence very hi idle.
I'd suggest that you put remote in neutral, raise idle/start lever and look at cables on engine. Then lower lever and look again. (non-running engine) It should have pulled the lever on the engine up against the idle screw.
I'd advise against shifting a running engine at high idle speeds. I choked mine down to a respectable idle before shifting fearful of gear teeth or shaft breaking.