I use a 14mm Crows Foot on an 3/8 Extension to loosen and tighten the Idle Screw Nut.
If it is still there the Idle Speed is listed on the Emission Sticker on top of the upper Cross Member that is in front of the Radiator. Also on the sticker is your Valve Clearances and some timing information.

Attached Thumbnails

 

__________________
84 300D, 82 Volvo 244Gl Diesel