Thanks, Dalton--yours is the reply I was looking for! I suspected Lambda related to stoichiometry. It's a '95 E420. Also has recent caps, rotors, wires, and plugs.

Which vacuum hoses are suspect? I replaced the thin clear one between ignition advance module and the intake manifold when reinstalling the ETA; it was very brittle.

Where is the FP regulator in this car?

Thanks again--