Whats this -(M103 rough start)
 

I have a loss of manifold vacuum (visable on the economy gage) just after start up that is occurs about 50+% of the time. It only lasts 15-45 seconds and then the car runs and idles well. I also have a little clattering lifter, or something (not familiar with what sounds like what), that seems to hang around intermitantly until full opperating temp has been reached.

My theory: Could these symptoms be caused by tired old valve seals and a moderate valve cover gasket leak?

I forgot to mention I am running slightly high opperating temps 95-110° C.
Due either to a bad viscous fan clutch or a partly blocked radiator.
And up above 100° C I sometimes get a little oil pressure surgeing at idle (1.2-1.8 bar).

update
 

This thread is now accepting wild theorys as well as sage advice.

So does the car seem to miss on a few cyllinders after start up, or is it jst rough? The vacuum gauge in the instrument cluster isn't a good tool to use for diagnostics. Does it happen durring cold, or hot starts?

Fuel pressure may not be high enough or you could have a leaky injector? Fuel dizzy could be leaking, injector, injector seal pump, who knows. Fuel relay maybe? Dirty air flow meter? I'd clean up the AFM well and run a can or two of SeaFoam through the top end to burn off a lot of that carbon in there and then see what happens.

New fan clutches are cheap, get one to be smart. It's probably been replaced once back in the mid 90s and it's due again (I figure stuff like that is good for 10yr/100K or so). Then you can see if the radiator is bad. Again, it's 20 years old there... so you may want to pick up one for piece of mind. I did for the SD and the 420, SDL has the newer style alread. I'd flush that coolant out as it's probably the green crap and get the proper yellow stuff in there.

Valve cover gasket is cheap too and will take maybe an hour to swap if you have a few beers during the process. :)

The valve seals seem to leak on the early M103s, this is more pronounced at higher RPM such as freeway driving. I think they're 4-6 hours to R&R. Since you're at 200K you may want to consider having the head rebuilt if you have the time, money, and resources. Then you could get new guides for the chain in, tensioner, etc.

Hit man X,
Thanks for the good sound guidance. Its stuff I know needs considered but the car is running pretty well over all. I am tryig to assemble the rest of the seals I will need (Ihave the front U, the VCG, and the cam seal already), the MB sealant, the chain guides, and the know how. My plan would be to then tackle the upper top end and measure for streach. In the mean time I am just a little curious about my symptoms.

GVB,
It's not missing just wants to stall out unless it gets a little reving out of the gate. And it's only on cold starts not hot ones.
The water temp sensor is just a little over a year old... as is the breather hose between the air cleaner and valve cover.
The O2 sensor is about two months old as are the other breather hoses AI to VC, and either side of the ICV.
Duty cycle is in the 50-60% range.

bump

Is the airplate clean?

Not particularly. I wiped down the surface of the plate and the inside of the neck with the plate depressed and my towels got dirty. Whats the proper solvent?