Prevent porting of vacuum to the EGR to prevent it from ingesting exhaust gases at partial throttle - a common "fix" for diesels.

While this is likely to help some diesels, it probably does little for a gas engine car ... as you can tell, it is obviously not the problem with your SL.

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George Stephenson
1991 350 SDL (200K and she ain't bent, yet)
former 2002 E320 4Matic Wagon - good car
former 1985 300 CD - great car
former 1981 300 TD - good car
former 1972 280 SEL - not so good car
a couple of those diesel Rabbits ...40-45 mpg