As AJ's said, the bushing should be hard clamped by the bolt between the tabs, once it is torqued to the spec of 60 ft-lbs +/-. All of the motion should just be in the rubber around the bushing, or the rubber inside the arm casting. If it is moving up and down any, then the idler arm bolt is too worn (look at the underside of the head), or the tab holes are wallowed out and are worn smooth and the bushing is not being hard clamped in place.