400 E problem

[x8m]

I have a 1992 400 E with 190,00 miles that emits black smoke from the exhaust while idling. Also, there is soot falling from the exhaust. I have replaced several items mass air low sensor, some parts I can't even remember including the wiring harness under the hood and the probelm still exists, does anyone have a cure for such a problem?

Thanks,...