photo/location of "fuel pressure relief valve"

[kuene]

Hi. I've been doing a lot of thread searching around my hot rough idle problem. I don't think I have any air leaks in the lines running in/out of pre-filter (though I intend to eliminate this possibility), and I have a new rack damper that was installed last year when I had my valves adjusted. I'm going to fiddle with the rack damper bolt, but I also wanted to check this spring folks have talked about stretching that is inside of the thing described as a "fuel pressure relief valve." I have an 82 300d.

First question:

Where do I locate this valve? On the injection pump? Next to the spin on filter? Could anybody provide a picture of where I find this?

Second question(s):

I am going to fiddle with my rack damper bolt after I inspect this spring. My idle, measured with a strobe tach at the fan at about 710rpm, so I think I'm within range, unless this is a bad way to measure rpm (my gauge is useless at anything below 1000).
1. If I have a rough idle when hot - should I try turing the rack damper IN or OUT?
2. How many turns are in this thing? Do I try just small, quarter turns at a time, or multiple turns at once if I want to notice any difference?
3. Would I notice any potential change in idle immediately (assuming I was turning while engine was hot and roughly idling?

As always, thanks for wisdom!