I doubt
 

it cured a rough idle but I'm sure it idled quieter.

OK... Nate gets a trophy on this thread... post number four should have caused several of us to ask what Nate just mentioned... and is spot on concerning the high idle hiding something else....

What spin on filter are you referring to in post #12?

OK, now I get it. The spin on fuel filter. Forgot about that one.

Anytime that filter is off the car... or being replaced.... fill it with Diesel Purge just SOP. Dump the rest into the tank...

I had the SAME issue with my car.
It would idle smooth at one stop light, and idle like a shaky old turd at the next. Sometimes it would ilde smoothly and then slowly start rocking. Once the rocking started it would get worse and worse until the whole car was rocking side-to-side.
Embarrassing; folks behind me could definitely see Betsie rock side-to-side like a cradle, and I was getting seasick. I would drop her in neutral and manually raise the RPM's a little with the throttle pedal whenever that happened.
I had already changed the engine mounts. That did absolutely nothing.

Solution:
Rack damper bolt. Tightened it up a little (adjust with engine hot and running) and no more shaking ever. At first I had tightened it up a bit too much, which results in the engine surging at low throttle input and the RPM's dropping too low when it goes from load to idle (it would almost stall out for a split second every time I release the throttle).
So loosened it back up again. There is a quite delicate balance between the car shaking at idle, and between RPM's dropping to much when releasing the throttle so it requires some messing about.
End result though is smooth idle and a responsive engine.

That rack damper bolt was designed into the system by OCD Germans to allow for taking up wear to the system.... so that will probably fix the problem as described... however, still need to check the valves cold.

@leathermang
Right. Your engine needs to be in relatively OK condition for the rack damper bolt to do anything. It's an adjustment. It won't do anything when things are way out of specification.

As far as I know my rack damper bolt has never been adjusted since 1981. So where do I find it and is it so touchy that I should just accept the rocking? Got a pic?

And, yes, I have sat at stoplights with my foot on the brake and the accelerator at the same time to stop the rocking. Deja vu. Probably should do in another thread so we do not steal Otto's thread.

So, you are in the 98 percent with the rest of us ...
and True....

@Tyl604
Yes, start a new topic to talk about the rack damper bolt. It is a really easy adjustment. You do not need any specific tools (just a 14 and a 12mm wrench) and it's easy to find and easy to get to. You can't really break anything either - if you happen to adjust it too tight your car might be hard to start and it'll almost stall when coming down to idle from higher rpm's.

The bolt is on the back of the IP. The IP is that long straight thing at the drivers side with all the hard fuel lines coming out. The bolt is right at the back, right in front of the oil filter housing.

The procedure is quite simple:
You make sure the engine is nice and hot, and then with the engine running you loosen up the lock nut (counter clock wise, 14mm wrench, you only need to loosen this up like half a turn, don't go crazy unscrewing it, not neccesary) and screw the rack damper bolt in a little (righty-tighty, 12mm wrench)) very slowly until your engine suddenly smooths out. Then with the 12mm wrench hold the damper bolt in place as you use your 14mm wrench to tighten up the lock nut again.
On my engine the engine will instantly become smooth when adjusting the rack damper, ie: It rocks like a turd, and as you adjust the bolt, suddenly it will be smooth. This is the sweet spot. When you back it out 1/8th of an inch, it'll behave like a turd again. At least, that's how it is on mine. Any adjustments further then the sweet spot can cause issues. On my car the engine will start to surge (rpm's going up and down constantly) with small throttle input when the rack damper is in too far.

It might be best to have a helper who can sit in the car, with the transmission in Drive and their foot on the brake to get the best adjustment. As you are moving the rack damper bolt in, you will immediately see (and hear) the change in idling, as your rocking engine will smooth itself out.

Since my wife absolutely refuses to have anything to do with Ol'Betsie (she won't even ride passenger in it, she hates it from exhaust to grill:(), I adjust the bolt with the transmission in Neutral. It just requires a bit more trial and error this way.:)

Ceristimo - that is exactly what I need. No need for another thread.

Thx.

My wife feels exactly the same; I tell her I will get rid of the SD when it dies and have been saying that for 20 years.

It only took three hours for this thread to get hijacked. I adjusted my updated rack damper bolt a couple of years ago when the car was stalling after exiting the freeway. I've had a broken air cleaner mount several times since and it never caused rough idle. One way to resolve this would be for me to remove the mount I just installed and let the cleaner flop around and see what happens to my idle. I don't really feel like testing fate right now and after spending the last two weeks wrestling with my AC system I'm taking a little break from doing anything under the hood.

The car stopped shaking after I replaced the mount, that's all I know right now. To be honest, the rattle wasn't even that loud.

Where exactly do you think it was hijacked ?
The original question / link to high idle and stalling was very strange... air cleaner mount... ?
people talked about things that might affect that idle , stalling situation..

Post #23, but it doesn't bother me. These threads usually go in different directions and I'm not even looking for an answer, just started the thread to point out something odd that happened with my car. Maybe some piece of gunk in the tank strainer broke loose right after I changed that mount.