A couple of local guys showed me how they "check " their engines
snap the throttle stick back and forth and expect the engine to follow.
they actually thought that was how you determine if it is set correctly!
The same comments about needing a fast throttle servo.
Good , even geometry on the linkage - low drag /ZERO slop linkage , is many more times as important.
My own setups use a low cost digital servo for throttle .
these position much more accurately.
JR has a new one for little money -