If you are using the torque give in the manual, which it sounds like you are, and if the arm subsequently binds up, then I'd conclude something is wrong in the assembly. I've only had the older style 230 idler arm apart, and it's a funky mechanism. I don't know the details of the later 280 design, but have replaced may idler arm bushings on other cars and there is a certain sameness to all of them. They typically are stiff, but you should be able to move it back and forth without a huge effort. Perhaps a spacer washer is missing? Maybe the bushing isn't pressed into the arm properly? BTW, I've never seen one (other than perhaps the 230 variation) when the drag is set by the torque on the nut. On all that I can recall, you crank the nut down tight. So it doesn't sound like you have a torque problem, but rather an assembly problem. At least that's where I'd be looking.