Chassis221:

I unplugged the O2 Sensor and drove a mile with horrible misfires. I removed the O2 sensor and drove 5 miles at BREAK-NECK speeds without one misfire! Catalytic Converter it is! Thank you so much for the input and help diagnosing!

 

cool im glad it all worked out for you...glad i could help you!! your welcome!

 

O2 sensor it is and for sure! How long ago did you changed them? I have 172K on my 99ML320 and it was doing the same thing only upto about 4000 RPM. Compare to yours, I also changed all 6 coils and wires the fuel rail with injectors and MAF sensor all oem parts just to find out that it has nothing to do with my misfiring. I have the original cats and small fuel filter that I was going to upgrade with large one that is in my tool box for over a year with fuel lines, had no time for it but now I know that it is not the fuel.
Adventually, you will see code P0150 and later P0130 that will come up with these misfires. Both of them went bad (well not bad because I also could adjust my driving that I would never see a CEL to pop up) within about 2K miles.
After changing both front oxygen sensors (Bosch 13782 or 0258003782009 or 000 540 8117), car is running smoother then ever, has plenty of power to waste and when I gun it or take it into higher RPM, it acts normal and never seen the CEL to come up again.
I bought one from local creigslist for $50 and the other one on e-bay for $70 with free shipping from Canada.
I posted my problem before but no help and every one pointed at my old little fuel filter.
Last month I was pulling two axle trailer with Dodge Intrepid on it, maybe 6,000 lbs. or more in total and had to floor it few times because of the highway constructions. It was week after the second O2 sensor was replaced (it took me 15 minutes with lifting up the front of my car to swap them but make sure the exhaust is cold).
You can trust me on this one!!!!!!
Bernard