To lube the cable you will need to remove it again and take the cable out of the throttle. Hold it upright and very carefully let oil of choice go down the cable. Stop occasionally and work the cable in & out. Do that a few times. Hope that poor description helps a liitle.
But as you disassemble check the following items :
Make sure your grip or hand guards are not hanging your throttle up causing resistance. Also verify your cable is in the guide track properly and the guide is not grooved and causing you the resistance.
Good luck.