I just took a set of platnium +4s out of my 300E and put in the correct H9DCO plugs and the intermittant rough idle seems to be gone. I did not realize my independant mech had put in the +4s
over two years ago and have suffered with the rough idle ever since.

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Dave
88 300E 250K Sold
2000 C230K Totaled @104K
2003 ML320 156K Sold
2009 E350 4Matic Sport 46K Sold
2011 ML350 60K Sold
2014 GLK350 46k Sold
2012 GL450 67K
2016 E550 Cabriolet 48K