The hand throttle on our trucks pretty much all operate all the same way, after you start the engine (cold) pull out the throttle to maintain your RPM at say 800 RPM, keeping any eye on things because as the engine gets warmer it starts to run more efficiently and your RPMs will keep going UP, actually this will happen fairly fast if your not paying attention. After the engine comes up to operating temp I then just pull the hand throttle out to my desired RPM, say on my M-920 and I want to run the rear winch, after engaging the PTO I use the hand throttle to bring the RPM up to 1200 RPM and then take care of any winching I need to do, these trucks after up to operating temp will hold RPMs very good. I am not an expert on your situation at all but it sounds a little like you have something else going on? I am sorry I cannot be of more help to you?
Karl