The spring will work, but another option is to epoxy a Nylock locknut to the throttle linkage so it holds the idle speed screw at whatever place you adjust it. It's a simple, permanent fix that doesn't look out of place to the casual observer. Install the nut with the nylon locking insert away from the linkage and use something like J-B Weld to attach it to the throttle bellcrank.
Jerry

"It is better to be silent and be thought a fool than to speak and eliminate all doubt!" - Abraham Lincoln
Cringe and wail in fear, Eloi- - - - -we Morlocks are on the hunt!
There is nothing noble in being superior to your fellow man; true nobility is being superior to your former self. - Ernest Hemingway
Love your enemies and drive 'em nuts!