Hi the failsafe should fit between the reciever and the throttle/brake servo.
its designed to shut the throttle in the event of signal loss from the transmitter or your reciever batteries going flat that all !
go to the mtronics website and download the instructions for your fail safe www.mtroniks.net .
its sound like you idle speed is set to high thats why is creeping off.
hope this helps
i agree its down to preference at the end off the day , but when youve walked down to the local park( 1/2 mile) and then snapped the pullstart on first pull its a little frustrating to say the least lol