Pushing the plated was suggested in an earlier post, and when I did it the duty cycle reading did increase immediately, to about 91.4%, before the engine shut down in what seemed like one second. So, summing up, since there was a change in the duty cycle reading, the problem is the constant false signal from the O2 sensor telling the EHA that the mixture is too lean, and by responding appropriately the EHA actually causes an overrich mixture which can't be effectively overridden by adjusting the mixture control screw. Thanks so much. I'll try to take care of this over the weekend and report back.

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87 300e (white/black; amg body kit)
88 300ce (red/cream; amg body kit)
93 300ce cabrio (white/blue/blue top)
93 300ce cabrio (black/grey/black top)
98 ml 320 (totaled @ 137,000 miles)
99 clk320 (black/grey/black top)