Nice stable of vehicles there Troy! I am not a mechanic, so if I were in your situation, I'd have the E420 diagnosed by someone who is. The last time I had my E430 looked at (Check Engine Light) a dealer told me up-front that there was a $95 charge. I went ahead with it, and they found a faulty O2 sensor; they had the part so just had them replace it.
Going to a dealer is probably NOT going to be the least expensive solution to your problem, but IMO, you WILL get to the bottom of it.
Paranthetically, out of your 3 fine autos, I think I would fix the Benz and trade your BMW
