Oh great, another annoying vacuum problem thread! I've been searching for a while now with no success, so I will explain wtf is going on. Idle shakes pretty hard, probably gonna kill my new motor mounts. Hooked my vacuum system right at the main line to my boost gauge so I could see how the vac system is working.
System leaks down pretty quick, like just under a minute. System never builds up past 10 in/hg.
One of the AC pods was leaking, I plugged the line. Other pods hold strong vacuum over lunch.
Door locks also work consistently even when parked over the weekend.
Reading it might be the check valve, I took it off. The o-ring was shot, replaced previously by former owner. The valve itself was intact, spring, plastic and all. There was some motor oil in it though.
I bypassed most of the lines under the hood. EGR deleted long ago, also got rid of the loop. Vacuum dampener is hooked up, new fittings for a tight seal.
I'm not 100% but I'm guessing the presence of MOTOR OIL inside the main check valve is a hint of the issue. What I don't know though is what is inside the pump that would need to be resealed? I know the older versions had a diaphragm where the newer style uses some sort of cam.
I'm sure I have a leak somewhere else (maybe a missed fitting or something).
Help?

Update 1/28/17
New rack dampener bolt, not 100% sure if I needed it, new one was stiffer than the old, but not collapsed. No change

Adjusted valves .15mm intake .35mm exhaust. No change noticed, 6 of 10 valves tight, 2 loose, 2 perfect.

Vacuum pump by itself takes over a minute to get to 10 in/hg vacuum. Leak test performed at dampener, the two little green things, and modulator, all passed. Door lock system passed, HVAC small leak, very slow. Seem to have no line for a reservoir, maybe removed by previous owner? Didn't test shutoff (works great) or vacuum control valve (I read it's supposed to bleed off into cab). Rest of system deleted.

Update 2/1/17
America is still here, Donald Trump hasn't blown it up and most of us are living our normal lives.
New vacuum pump confirmed to be working properly, pumping a nice strong 23 in/hg.

A while back I used the guide here:

Mercedes Vacuum Troubleshooting

It will take you step by step through the components to check. First checking your pump then going from there down the line of related components. Things need to be done in the order described in the guide otherwise your just going to end up chasing your tail.

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Old Blue - 83 240D 6 speed manual trans, OM648
Green Machine - 2001 Europa G500
87 300SDL Bought on Peachparts. Low-ish miles..?

Family Truckster - 2012 VW Touareg TDI

Patchouli Wagon - 2004 E500 - SOLD
333k mile 97 BMW 750il V12. - SOLD
The Californian - 85 300TD - SOLD
Daily Super Sedan - 03 Audi S8 -SOLD

Seems unlikely that bad vacuum pump could get oil into the system, since it sucks from the system, and sits lower. Usually, engine oil in the vacuum hoses is from a bad "shutdown valve", which bolts to the rear of the injection pump. Indeed, many of us install a small clear filter in that hose to monitor any oil. The other way to tell is when oil gets sucked up to the key switch and starts dripping down on the driver's foot, which is a big mess at that point. You can use a small "fuel filter" for garden equipment, or some VW shops stock them.

To speed up testing, you can block off large sections of vacuum users. To test the pump alone, disconnect the main tube and connect a vacuum gage alone to it. Re vacuum flow, there will always be some flow since the VCV (above IP) seeps in air as part of normal operation. That should be a thick black tube that goes into the cabin w/ a clear filter in the path. Many people pull it out by accident, then ask "what did I disconnect?". The tube is supposed to open on the cabin side.

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1984 & 1985 CA 300D's
1964 & 65 Mopar's - Valiant, Dart, Newport
1996 & 2002 Chrysler minivans

I can't remember how many other valves besides the screw in Check Valve are actually inside of the Vacuum Pump. But they are disc valves. But I would suppose that Oil in them might cause them issues since the springs on the interior valves are not very strong.

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84 300D, 82 Volvo 244Gl Diesel

Thanks guys for a good starting point. I did check the vacuum the other day with the accessories and all disconnected, just the booster hooked up, and was still reading 10-12 in/hg.
So from what I am reading, the only way oil could get into the system is through the shutoff valve? It works well, immediate shutoff. Is there a seal that can go bad, or does the whole valve need replacing?

I'm not understanding the correlation between severe idle shake and a vacuum issue.

For severe idle shake, the very first thing I would be looking at would be a valve adjustment. Maybe even a second one about 200 miles later if they were tight and needed adjusting.

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Sam

84 300SD 350K+ miles ( Blue Belle )

The bad idle shake surfaced its head around the same time I noticed my brake petal being hard to press upon initial startup. Could be two different issues, but odd that both happened at the same time.
Oil change and valve adjustment is on the docket for this weekend. Last two changes valves were perfect.

In a gas car, a bad booster causes a rough lean idle, at least in old carbureted cars that couldn't compensate for the extra air flowing into the intake. But, no such thing in our diesels. The vacuum pump expels air into the crankcase, at least the 1-tube type does.

Before condemning the vacuum pump, test it alone. It is common for brake boosters to leak enough to affect it. Unscrew the metal fitting near the power steering pump and connect your gage to the tube. I assume you have a bag of assorted rubber hoses for such things, as I do. If not, start collecting. Hand vacuum pumps usually come w/ a bag of rubber adapters too.

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1984 & 1985 CA 300D's
1964 & 65 Mopar's - Valiant, Dart, Newport
1996 & 2002 Chrysler minivans

Ok, tested the vacuum pump by itself. Cold start, erratic between 5-7 in/hg.

The vacuum pump should produce 18-22 inch of vacuum. I would recommend that you replace the vacuum pump with a new genuine MBZ pump. Vacuum pumps do explode internally and when they do they generally take out the timing chain, camshaft, and other major engine parts. A quality rebuild kit is about the same cost as a new pump. A new pump also comes with a new check valve. Cheap insurance to replace the pump.

Search around for a pump. I found a new pump by the OE manufacturer for not much money. It may have been a fluke but price was 1/2 of what other places want.

Be sure that you tested correctly with the pump completely isolated - ie at the pump itself with the line to the booster removed. Clean the bolt heads and tap the socket in. You really don't want to strip the heads.

When you start testing at reinstallation, disconnect and test each circuit independently. There are lots of diagrams available and it is not complicated. You can use air brake hose to replace the plastic lines if need be. It is tuff stuff and will last longer than you own the car. Just make sure every joint has a tight seal.

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85SD 240K & stopped counting painted, putting bac together. 84SD 180,000. sold to a neighbor and member here but I forget his handle. The 84 is much improved from when I had it. 85TD beginning to repair to DD status. Lots of stuff to do.

Regarding Bill's shutdown valve post, here's a link on how to replace said valve, should you need to.

How to Repair Your Shutoff Valve

Thank you for that link. I'm sure I will need it one day.
I ordered a vacuum pump, should be here next week. Hopefully. Thanks for all the tips.

Are we talking about W123 or W124 here .

W123 chassis mate, it's an 85

Anyways I adjusted my valves today after my oil change. 8 of the valves were on the tight side, all good now. Still a shaky as heck idle. Still good across the power band.

For the vacuum issue, still no change as my pump has yet to arrive. Going to get a fuel pressure gauge and test out my lift pump, make sure it's ok.

What is factory spec for the lift pump for flow rate and pressure?