I wouldn't run platinum plugs in any 1990 MB, they suck. Use the updated Bosch Copper Pluses. My 1990 300TE was running like crap and I discovered the previous owner had installed Platinums in the engine....I did nothing else but replace the plugs, this was last October and the car has run perfectly ever since. This idiot also had put synthetic oil in it as well. Swapped that out for the real stuff and the oil pressure gauge went from virtually 0 to 3 bar immediately and has remained there ever since. I wouldn't mess with original factory specs. Bad way to fly.....trying to fool mother Mercedes.....