If your 82 300SD has original equipment throttle linkage like mine and all the cars used for pictures in the Mercedes factory shop manual I bought from mercedes, then the transmission "shift cable" is a cable which travels from the right side of the transmission, is attached midway to the transmission filler tube, and is then connected to the THROTTLE linkage. The original equipment vacuum valves on the valve cover control vacuum to the EGR only. However, they affect shift to the degree that they (or the connecting hoses or the EGR)leak. For example, air leaking through those valves would reduce vacuum at the modulator. But maybe you have some unique, mickey mouse arrangement put there by a previous owner or mechanic who didn't understand how the system works. If that's the case, we can show you pictures of how it's supposed to be. Good luck!

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'82 300SD - 361K mi - "Blue"

"Good judgement comes from experience. Experience comes from bad judgement."

listen, look, .........and duck.