Another thing I just thought of that happened to me that you can check-

You say you just did a valve adjustment. I would go back and double check the clearances and the pattern of exhaust/intake is correct. It shouldn't take more than a half hour to check. One time I messed up the pattern of E/I and I couldn't start my car in 20F weather unless it was plugged in. Redoing the valves correctly solved the problem.

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2009 ML320 Bluetec
1985 300CD
1981 300TD

Past Mercedes
1979 300TD
1982 300TD
2000 E320 4Matic Wagon
1998 E430
1984 300SD
1980 300SD