Not much left to check.

Air Leak?

Low Fuel Supply Pressure?

Or:
Long Fuel Pressure Relief Valve/Overflow Valve Thread
Fuel pressure relief valve adjustment - PeachParts Mercedes ShopForum

Just an update, I replaced the motor mounts, one of the engine shocks, tranny mount, and adjusted the current rack damper bolt.
All with no luck :(

Going to try to find a new rack damper bolt at the pick n pull tomorrow.

I see a tiny amount of fuel around a couple of the injectors. Fuel lines are new, maybe the hard lines are leaking a tiny bit?

I want to try this as I'm also only getting about 22mpg highway. How do I find the relief valve? I've been poring over the threads and there's lots of useful information but little about where it's located or what it looks like.

It's inside the lift pump somewhere?

The RD bolt (pin) may be just as worn out as your current one.

They are available new, I think, check the buy parts button at the top of the page.

Rack damper bolt/pin #000 074 26 74 and
the seal ring # 002 997 85 45.

If you're referring to the item in the pic, that won't cause low mileage.

Make sure your odo is good, check for fuel leaks.

If it's the newer (gold) style, then it shouldn't be. I don't want to spend $50 on a new rack damper bolt if that's not the problem.
Also, there was oil on the old one when I removed it, I'm guessing that's normal?

In the thread that diesel911 posted above, some folks reported an increase in fuel efficiency.
That's less my concern than the hot idle shaking. Looks like the valve came out of the top left part of the lift pump?

Yeah, a gold one should be okay, there'll be oil on it. Pull it and see how much pressure the pin takes before moving, should be pretty stiff.

Actually, my lift pump doesn't look like that. I pulled the banjo fitting and bolt off the backside of the IP and the bolt looks just like that one in the photo. The spring seemed to be in good shape but I tried to stretch it a little bit just in case.

Pressure on my current one is pretty good, about to head to picknpull, keepin my fingers crossed

So no gold rack damper bolts at pick n pull :(

There was a steel one that had lots of room left to be screwed into it's current IP and the spring is definitely stiffer than the current one. (although I pushed and not pulled, should I try the latter?)
Didn't make any difference.

I also tried a compression test today just to make sure. Glad I did because I was pleasantly surprised:
440 415 440 405 420 (front to back)
It's only got 153k miles on it but does have some blowby so I was expecting a little lower.

The cylinder with 405 compression (#5?) had a little bit of oil on the glow plug when I pulled it. Is that anything to be concerned about?

There's still a small amount of fuel accumulating around the injectors that concerns me.

I'm going to try to track down a gold RD bolt I can borrow from someone, but this really seems like a fuel issue to me. IP timing? Fuel pressure?

Adjust the valves and check the compression again, if you hadn't before the first time.

Already did. They were very tight. See post #7

Broke down and paid $67 for the new rack damper. Lessened the shake a little bit but not much.

I also replace all my injector return lines as they were starting to leak. I'm getting a buildup of vacuum in the fuel tank, I guess I have a clogged vent line. Doesn't affect the shaking if the fuel cap is off, though.
But, I think the pressure was causing the injector return lines to fail prematurely. When I started taking them off they were gushing fuel like I've never seen. When I pulled the fuel tank cap off the gushing stopped.

If I pump the primer pump I can hear air coming from somewhere around the IP but can't tell where.

This is driving me nuts

Oh, and all the fuel lines are good, no leaks. I also made a fuel tank in a jar to eliminate everything below the lift pump.

dang it, I read through this cliff-hanger and found that the last pages are all torn out...any conclusion? I might be stuck in the same novella myself, so I'd like to know how it ends.

Upped the idle a little bit and that's about all.
The shake went down a little but I ended up selling the car like that, I don't think the new owner even noticed really.