1990 Mercedes Benz S500

Engine Performance problem
1990 Mercedes Benz S500 V8 Two Wheel Drive Automatic 95000 miles

We have a 1990 560 sec. We do not drive it in the winter and only slightly in the summer. The mercedes dealer says the car is carboned up and gave me some fuel injector cleaner.
We took it on the highway for a short run but still blows black. Would really appreciate some advice !
Rodney in Canada
April 20, 2008.

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