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,...

had the same problem with my 92 400e at around 160K. Thought it was gonna cough up a lung. My problem also included a general loss of cold idle and low idle. The car would stall and/or cough up black smoke..Here's what I found and it fixed the problem.

There is a vacuum hose that runs from the driver's side fender well to the back of the engine under the intake manifold. The module on the fender well has something to do with air/fuel mixture and/or idle and throttle position. bottom line, the line on my car was brittle and cracked..hence, it would not hold the vacuum.

I think i used about 1 meter of vacuum line (get little extra for good measure from your benz shop)

took me about 30 minutes to carefully snake the line from the fender well to the back of the engine.
NOTE: the line runs from the well bwteen the power steering pump cannister, under the distributor cap housing and then under the intake manifold to the back of the block. I was able to reach between the firewall, behine the throttle linkage to reach the connnection point. There is a small 90 degree rubber connection tube that hooks the line to the block.

Repalce it, fire it up and run her around a while. Mine seemed to improved over a series of cold starts and idles. after a few days, no problem !!!! Good luck.

__________________
Jeff
'87 300E
'92 400E
'06 ML350