Posting this because someone else may find it useful.I rebuilt the poppet cam with new O rings Vacuum diaphragm etc. The old diapraghm was trashed...it ran great for a day or two than started loping again...It was driving me crazy I double checked everything and finally took the Poppet assembly apart again only this time I took the snap ring off the plunger part and disassembled it...the little spring inside had snapped in half coiled around itself and was now half its original size. I went to hardware store and found one the same dimension and approximate springiness cut it to the right length and put it all back together...she purrs now without a hint of loping. Wanted to share this because when all your vacuum fixes are exhausted...check inside there! In all my internet searching I havent seen this problem.

Could you be a little clearer on this? I have a 72 250C which tends to lope. I realize your car is a diesel, but perhaps they might have this feature in common. Are you referring to a component located under the valve cover, as part of the camshaft assembly?
Thanks!
Ken

The OP is talking about a small shaft on the backside of the 220D OM615 diesel injection pump. The engine governor on these engines is based on a vacuum signal from the air intake, so if you have a leak around this shaft, the vacuum signal gets messed up. While I have virtually no familiarity with your engine, I doubt there is much in common on this specific issue.

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1968 220D, w115, /8, OM615, Automatic transmission.
My 1987 300TD wagon was sold and my 2003 W210 E320 wagon was totaled (sheds tear).

No relation to anything on a gasser. As far as the engine goes. This is small spring inside thegovernor on the diesel injection pump.

Actually inside the governor...not the shaft or large diaphram spring

any chance you took some pictures while doing the repair?

I did not take pictures however its easy to explain...remove the four flathead screws on the very back of pump its a pain in the butt but you can do it without removing the whole pump...just use the right length screwdriver and have strong hands...dissconnect the one lingage rod and remove the whole assembly...remove the two smaller 8 mm bolts from the back of assembly and it will expose the poppet cam which controls the linkage arm remove the small bolt holding the cam to its axle and slide the axle out...this is a good time to replace the O rings and washers on the shaft...I found them at the hardware store in the plumbing stuff...you will see a larger plunger with a small one inside it...remove that snap ring and the spring is under the smaller plunger...take photos so you can put it back together right...