My 86 420 idles really rough. It is also intermittent. Sometimes it will be smooth, and sometimes not. I tried fuel injector cleaner gas additive and it seemed to help at first, but then it would go right back to idling rough even when I am still using the stuff. Is this an ignition problem? A fuel system problem? Thanks for any help.

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'86 420SE Euro
904 Midnight Blue, Gray Velour
Dad bought it new, now I own it.

"A Mercedes-Benz is like a fine wine, it only gets better with age."