That sounds a lot like what’s happening. Doesn’t seem like one cylinder missing, all of a sudden it cuts out quite a bit. If you floor it, will falter a bit and suddenly surge. High end performance is still pretty good which leads me to think that the engine is in relatively good shape in terms of compression.

I checked the MPG, I’m only getting about 10 now, normally it’s 13 to 14.

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1986 300SDL, 362K
1984 300D, 138K