I've got a high idle knob in my 4 speed swapped Grey 82 300D.
The hole in the dash is there, all you need is the bracket, cable and such. literally fits right in.

I found one in a junkyard, pulled it because I thought it was neat and had never seen one. Got home, felt around on the dash and realized the hole was there but covered up with material. poked through carefully and installed it.

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1982 300D (w123, "Grey Car")
1982 300D (w123, "Blue Car")
2001 Ford F150 "Clifford" (The Big Red Truck)
1997 Dodge Ram 2500 12V Cummins
1996 Dodge Ram 2500 12V Cummins
Previous Vehicles:
1995 E300D, 1980 300SD, 1992 Buick Century, 2005 Saturn Ion