Sounds like you are just substituting S1 or S2 for the Throttle trim. Why not just use the trim lever? They even include a handy "Idle trim only" checkbox, so the trim only changes the low end of the stick, and doesn't change the high end.
On my gasser, I have 3 global variables defined, each controlled by a switch. Depending on the choice, it adds to the low end of the throttle - one as a very fast idle, used for initial starting, one a medium low throttle (needed when the engine isn't at full operating temp), and then the lowest possible idle, after it has come up to temp in flight and for landings. And then I have the normal trim, if for an odd reason it needs a bit of fine tuning. On glow, I just use the trim lever, set so at the lowest the engine will barely keep running. Adjust the trim as needed after startup for low dependable idle, which varies a bit due to conditions of the day. Then I have a switch set as "kill" that closes the carb completely.
Later edit: I got fancy above, because with the radio, one can. For the most basic - adjust linkages/radio so that at full down engine trim, the carb is completely closed. This allows you to kill the engine. Move the trim up to open the carb a little bit, for starting and then adjusting for a nice low, dependable, idle speed. Of course, adjust the high end, with the stick fully up, to completely open the carb. This is where the "idle trim only" checkbox is a great addition - moving your trim lever doesn't do anything to the high side, it only adjusts the speed on the low end.
Last edited by tedsander; 03-30-2020 at 07:38 AM.