YOU SHOULD NOT USE RESISTOR PLUGS ON MERCEDES!!! The ignition system is very carefully designed for use with non-resistor plugs. Resistor plugs add secondary resistance is excess of design specs and alter the secondary voltage wave form.

Sooner of later you will have problems such as rough idle or high emissions.

The proper plug is Bosch H9DC (NOT the HR9DC resistor type), and these are not commonly available at McParts, but are readily available for two bucks each from Mercedes parts specialists like Fastlane, which sponsors this site.

Any spark plug with an "R" in the designation is a resistor type and should NOT be used.

Duke