Did this problem start all of a sudden or did it get progressively worse?

Does it ever make it up to operating temperature? If so, does idle improve? have you done the nighttime water test on the plugs? What do the contact points on the inside of your distributor cap look like? The carbon formed on mine added anywhere from 7K-20K ohms resistance - a little dremel action took care of that.

What does your economy (vacuum) gauge point while idling? Have you checked your timing?

Pull one of your plugs and look at it. Is it black and sooty or white & ashy?

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A.S.E Tech A1,A6,A7,A8 & MVAC 609 + EPA 608

Unless stated otherwise, any question I ask is about my greymarket 1985 380SEL.