Last nite, after much counterclockewise screwing, I got the car to start reliably. I noticed something I thought very interesting. I increased the engine revs by moving the throttle linkage, and when I first touched the metal the duty cycle reading immediately jumped up to 64% and fluctuated around there. It struck me that this was like touching a radio antenna and getting better reception, ie, a bad ground condition might exist and be my problem. Where/what should I check?
BTW, this is not a CA car.

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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)