The first time ever changed plugs on any Mercedes was with my first MB, the 97 C280. I put resistors in. Mistake. Did not run well. I thought I broke an insulator or something (kinda hard to do when the things screw straight down from the top). So I bought another set! Then I figured something was wrong with my plug choice.

Then I found mercedesshop, read all about as a lurker back then, and went to the dealer and bought the correct plugs. Ran as it should after that.

As for plasma, etc, I don't know, but the correct plugs make things right. There isn't too much you can do on these cars cheaply that will result in improvement, as I have found out after owning these things for 10 years now.

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Thank You!
Fred
2009 ML350
2004 SL600
2004 SL500
1996 SL600
2002 SLK32
2005 CLK320 cabrio
2003 ML350
1997 C280 Sport