Yes, platinum plugs are not recommended for these engines. The techs that help out on this site won't help in diagnosing a problem unless the platinum plugs are replaced with the plain old copper core non-resistor type plugs. I think it has something to do with the electrode on platinum plugs being very, very small, and the electrode on copper plugs is much fatter.
I've searched before and asked the same question, and the throttle actuators are a common failure item on these engines, just like the mass air sensors.
There are potentiometers that go bad and wear out over time, as well as the harnesses going bad on these actuators.
2001 E430, Bourdeaux Red, Oyster interior.
1973 280SE 4.5, 170,000 miles. 568 Signal Red, Black MB Tex. "The Red Baron".