Max, which model of Loksound decoder are you using?
Also I have not found the need to add an idler on stock Weaver drives, but every Weaver Pittman drive I have seen had cracked sprockets causing very rough running and high load on the motor each time the crack comes around.
I use most of the tips and tricks here for smooth running:
https://bobsobol.smugmug.com/T...018664&k=jxLWMHq
HTH
Pete