84 300sd. I can’t seem to get the vacuum sorted out. Shifts aren’t quite right and I have intermittent trouble shutting off. Ive been through every connection and cleaned or replaced anything that was even half suspect including checking the connections to the ignition and that whatzamagig climate control thing under the driver side dash.
It also seems unusually sensitive to kickdown cable adjustments. A couple rotations either way and it behaves very differently.
To help diagnose where my problem I bypassed the “vacuum switchover valve” on top of the valve cover I did this by simply eliminating each T that sent a vacuum line to it and back from it from the area near the injection pump . The EGR had already been blocked off by a metal gasket but all vacuum lines to it remain. (testing purposes only of course)
Does that black box on the top of the valve cover only serve to control the EGR, or does it play a role in shifting and other vacuum functions? If it is there only to control the EGR did I bypass it correctly by just straight lining any lines that were going to it? Or, should I T together the vacuum lines that used to go to that box?

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84 300SD 274K
38K miles on flatplate heat exchanger and various diesel/veg blends. prior to that 4K miles on unheated veggie blends with kero and DinoD.