Well, I seem to have a resolution.

He whips out a hex wrench, goes under the hood for about .19026 seconds () and says, try that. It seems smooth as silk again.

I typically get about 20.5 MPG. With the too-lean mixture I used a full tank and got about 18.5 (which seems backwards -- ? ).

I'll update after a tank.

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1994 C280, dark green metallic
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(sold to another forum member)

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