Just got the car back (was out of the country...not that it took that long). I took the car to my local Autozone, and they pulled the codes, and found it was the O2 sensors. I took it back to the dealer and they installed new plugs and both the 02 sensors. Now it runs like a champ, has much better performance than I EVER remember it having.

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Mercedes Fleet:
2004 CL600 Designo Espresso SPORT
2004 S600 Designo Espresso SPORT/Lorinser Pkg.
1999 S320
1988 300TE
1972 280SEL 4.5
Diesel Fleet:
2014 GL350 Blutec
1987 300SDL Blk/Blk 4 place seating #18 head
1987 300SDL Smk Slv/Burgangy #17 head
1986 300SDL Blk Pearl/Palomino #14 head w/ 280K
1984 Lincoln Mark VII Fact BMW Turbo Diesel