One of the purposes of a failsafe is to activate when the radio signal is low or lost. So since you mention you are having a problem when the car is far away and it only impacts your throttle, I would say your failsafe is working as designed. I always check my failsafe before I start by turning on my car/radio then turining the radio off and checking my car to see if the throttle servo/ESC moves to the failsafe psoition. How far away is your car when you are having these problems? And what kind of radio are you using?