What exactly is this thing and where is it? The
idler arm is a fancy word for a bolt which ties the frame of the car to the steering rack. It makes sense, if the gearbox is supporting one side something has to support the other side, but what? An idler arm! What happens is when the rubber bushings get wear or aged they start making the car feel like a side to side swaying at slow speeds. This is caused by just that, the idler arm is allowing one wheel to move freely from side to side. You have to man-power the wheel quite a bit to see it move, but if and when it does move like that you know it is time to rebuild it. The test for this part would be to jack the front of the car off the ground and try to force the passenger side wheel to turn each way while watching the idler arm.