The plastic knob has already broken off when I bought my 83 240D. Per the tach I recently installed, it is idling at 700 rpm from a cold start. Turning the broken knob with pliers does not change the idle. It seems to idle fine but it is still warm (50 to 60F has been the coldest) but it will get much colder in the teens. What is the purpose of the idle speed knob? Is it necessary? Should I try to fix it? Is it a PITA to fix?

__________________
85 300D turbo pristine w 157k when purchased 167,870 July 2025
83 300 D turbo 297K runs great. SOLD!
83 240D 4 spd manual- parted out then junked