Straight from TIS, those numbers mean a specific section of the Torque Specification Document.
This is ONLY for N52 engine
, the 335i N54/N55 might be different.
Torque to 18 ft pounds for the tensioner, THEN torque it 90 degrees ignoring the torque. This is known as Torque to Yield or Torque to Angle, and I believe streches the bolt and allows for more consistency then if they just gave you a flat torque number.
No where in TIS did I find the specs for the idler pulley, but the idler pulley on the alernator is 40nm or about 30ft lbs so I'm going with that.