My 92 300-E (3.2 IL-6) idles rough in the hot summer months (runs fine at +RPM) but in the cooler
fall/winter months, the rough idle goes away or is less severe. Had the engine scoped out
by local MB-Dealership and no problems found. Was wondering if there is an O2 sensor or
some other "air mass" sensor that could be causing this problem. Or, is it possible that the
additives fuel stations put in the fuel in winter (emissions stuff?) could be helping the idle?
Plug #5 was a little oily but only 110K miles on the engine so it should be OK. No other
pressure problems, new plugs, wires, motor mounts, Cap & rotor are good according to MB tech.
Hummmm?

Thanks

 

WHat type of spark plugs?