One of our forum members said MB uses copper wire (I assume well-shielded), so my following comment is just a general comment on non-copper plug wires. A bad plug wire can sometime's be not noticeable on idle or on the mechanic's oscilloscope, but mis-fire under load. I've experienced this a number of time's with my previous Detroit Iron vehicles. They originally, though I'm not sure if my memory is correct, dubbed the carbon composite wires that replaced the copper wires "radio resistance" plug wires. You could hear each plug fire with a click on the old tube-style radio's used in those days, hence, the switch to composite plug wires. Another problem with the old copper wires in Detroit Iron cars was that if they weren't pushed in the brackets correctly and one got too near the exhasust manifold, or even the valve cover, the wire heats, thus increasing the resistance of the wire in a curvi-linear fashion.