Does anyone know of a quick and dirty way to properly set the fuel delivery at idle speed. (6 cyl) I am aware of what knob on the fuel injection pump controls this, I'm just not sure if I am running too lean or rich. My car runs great at highway speeds but spits and sputters (just a little) at idle. Just underwent a tuneup so I think I can rule out any electrical problem.

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2001 ML320
1987 560SL
1970 280SE
1965 230SL

For quick check at idle [rule of thumb ] without the aid of gas analyzer or vac gauge, you can use the tach.

the idle set is done only after you are sure of timing, dwell,
rod slop, idle stops, etc. are all in order.

With warm engine, the idle air bleed screw is turned for best
tach rpm. If rpm is on the high side, the mix knob on back of pump is too rich. If idle is low, mix is lean...
Remember that the pump screw can only be turned with engine stopped and pushed in to line up with drive slot in pump, Turn one click at a time .
Clockwise will richen mix.
CO on these is high compared to todays lean burners.
[ idle/800 rpm-3.5-4.5%.]
There are many other various rich running possibles, but this a bare bones test......as you asked for