While replacing the wiring harness, you may have disturbed the ETA cable as it runs across the top of the engine. The ETA cable has the same defective insulation as the wiring harness. Does your car have ASR? Maybe it's the ASR malfunctioning under acceleration. It's just a thought. After I replaced the wiring harness on my old 400E, my cruise control stopped working and I discovered that I had disturbed the ETA cable in the process. The ETA cable carries the signal from the computer module box to the EA/ISC/CC (engine acceleration/idle speed control/cruise control).

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1993 400E, 256,000 miles (totaled)
1994 E420, 200,000+ miles
1995 E420, 201,000 miles