using a Tachometer (Which your chassis has?)
So, the Mechanically "Set" idle might be a little bit higher in RPMs than the
specifications call for [you're having to allow for Air Conditioner engagement
"Drag" on the OM602.962]
I.E. if the specs call for 650 RPM,you might have to set it at 700-725 RPM.

No Performance loss/gain.

'holding the end of the set "Screw"
(Machine Screw with a Hex at the end)
loosen the securing nut and GENTLY turn the set screw in or out
UNTIL you achieve the RPMs desired
Re-tighten the Nut

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'84 300SD sold
124.128