Remove the idle screw. This isn't a weedeater plane is it? Thats what the servo is for. And screwing the idle screw in will only increase idle rpm by the way. Thats how they work!
Secondly why are you not running a kill switch? Thats kind of mandatory for club field safety. Otherwise, As you are taxi'ing your plane back to the pits your mates deserve the instant shut down a kill switch will provide.