FYI, you can unplug the ETA with the engine running. I did this on my 400E (non-ASR). The engine hunted around for an idle, but it did not stall. I suppose you could rule out the electrical function of the ETA as the cause of a misfire if you unplugged it while it was idling.

You can unplug it at the end near the module box. It has a spring-loaded canon plug that was engineered by Rube Goldberg.

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