g'day paul i have the same problem with the ute idler arm is brand new & with an air grease gun i cant get any in the only way i can do it is pull the idler apart & put grease in the threads then put it back together.
usually if they are low on grease they become loose & you can wobble the wheel on the side of the idler but i have seen them bind up from lack of grease as well usually in one direction only turn the wheel the other way its ok this can also happen when assembeling the idler by screwing the arm into the bush to far. hope this helps a little.