My 92 400E ran like crap when I got it. I replaced the caps, rotors, wires, and coils (some with known good ones to save $) and it made a huge difference. I was able to drive it daily. I also fixed the engine harness and put a new O2 sensor in and it runs even better. Still not perfect though-it runs rough until it warms up.

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1992 400E current
1988 300E sold
1973 280C totalled
1973 280SEL never got it running
1971 250C my first love but rusted out