Will, on a 82SD, both switches on top of the valve cover operate to control EGR. No EGR at idle or full throttle, and variable EGR at partial throttle. Because at one time I thought that these switches also control transmission shifting, I was hesitant to fool with them. Now, after studying the vacuum/EGR diagrams, I know that they are purely for EGR. Removing the cover and looking at the cams variably opening these valves will help in understanding. It's confusing though, because many people have reported fixing leaks in this area and getting better shifts. That's true, but not because they control vacuum to the trans. It's because a leak is being fixed, and that leak affects the transmission shift. The switch next to the thermostat simply opens up vacuum to EGR. Here's a siple way to test the EGR: engine off, connect miti-vac directly to EGR valve's vacuum port. Pump, release. Pump release. You should be able to hear some movement and see some too, probably with the aid of an inspection mirror. Does it move back and forth? If so, good, it's not stuck. You can remove the vacuum lines leading to the valve cover and cap them off. If it doesn't move, you can spray penetrant in there and maybe get it to move. A stuck open EGR will cause crappy idling and some high end power loss

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

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

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