Thanks to all. I hope I have the hot-wire type, but I guess I'll find out soon. The rubber hose on the purge valve has hardened (just like every other hose in my engine compartment that was once flexible), so I'm expecting to break it when I take it off for testing the Lambda.

Jim, I was reading your Menu 4(a) on MAF Contamination and Lambda under the headnote Fixing The Problem. Am I reading this correctly--that if Lambda is high (above 65%), you can disconnect the MAF at the canon plug and if that causes Lambda to drop to 50% then there is likely contamination on the MAF?

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