Dmitry, what we've been trying to tell you is that electrical arcing in the ignition system points to bad components. Whatever you can see that creates arcing sparks needs to be replaced. At first, it apparently was the coil wire and/or plug wires, and you took care of those. Right? Now it sounds as though the coil itself is suspect. As stated earlier, there may be other things going wrong that affect your idle condition too, but you can't really deal with those until the basic ignition system is in order.

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1988 California version 260E (W124)
Anthracite Grey/Palomino
Owned since new and still going strong and smooth
MBCA member

Past Mercedes-Benz:
1986 190E Baby Benz
1967 230 Inherited from mom when she downsized
1959 220S Introduced me to the joys of keepin' 'em goin'

There are only 10 kinds of people in the world--those who understand binary and those who don't