cruise control help please
 

new to forum and thanks for help. I have a 85 1/2 supra 2.8 inline six dohc. the problem is my speed control actuator is constantly pulling on the throttle gradually raising idle to as much as 4000 rpm. this is happening with the cruise off . is there a fix for this ? for now we have disconnected the vacuum line feeding it which fixes it. are these actuators repairable , is prob electrical or mechanical? help would be greatly appreciated. thanks jack l