ok, so this may sound really dumb and I don't mean to insult you, but did you pull/unscrew the little metal caps that are at the tip of the new plugs? I had the same exact issue after a tune up I did and went back and checked all my work and realized that these caps were on all the plugs that I just installed and it was affecting the engine with rough idling almost to the point where I was afraid to drive because I thought the engine would stall. again, not trying to insult you just trying to help.

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1990 190E 3.0L