My 190 idles rough as well, replaced motor mounts and every vacum connector in the engine bay as well as the heater valves connector. My idle smoothed up but still has a little shake to her. I am thinking now it is one of the two connectors going to the tranny, the one on the modulator and on the intake. Those are the only two I did not do along with the ones inside the car. The ones inside I checked and seemed fine, I did not check the ones in the center yet because there is a lot of crap to remove first. So I would check all you vacum connections, most of mine were dry rotted and starting to get little holes in them.

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~Jamie
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2003 Pewter C230K SC C1, C4, C5, C7, heated seats, CD Changer, and 6 Speed. ContiExtremes on the C7's.

1986 190E 2.3 Black, Auto, Mods to come soon.....