Carb....
Advancing the carb throttle without the timer?.....well not sure.
Spray something like carb cleaner or propane into the carb shaft at idle and report.
Might just be a bad carb.
What specific linkage are you talking about.
https://www.marineengine.com/parts/johnson-evinrude-parts.php?year=1996&hp=150&model=E150EXEDB&manufacturer=Evinrude§ion=THROTTLE+LINKAGE
You could also try eliminating the control box as a problem by starting it, disconnecting the red plug at the motor and see if it's still a problem.
Are your butterfly's opening all the way? I'm thinking they are.
Sorry, platform looked up for some reason. Try unhooking the temp sensor at the head. Unhook the wire and see if that gives you some joy. I.Boat system still won't allow to post pictures but it's part 28.