I own a 2002 ML320 my problem is that the car runs terrible, my scanner shows number1 and number 5 misfires also it says there are numerous misfires as well. I replaced #5 and # 1 cyl. coils as I was told that should be the problem well that had no effect on the car. I have also just replaced all the spark plugs. Any one that can help with advice I would greatly appreciate

 

Yes, had the same for a while especially on hard accelerations. Adventually, you will get code for the front O2 sensor heater circuit. I have new plugs, coils and wires, even new complete fuel rail, all parts OEM but still would misfire ones in a while. Finnaly, I got code P0150 with all P030X codes and replaced precat oxygen sensor to find out that the car started running better. After two month I got codes for misfires with P0130 and replaced the other front oxygen sensor.
Now, the trucks runs perfect, smooth with more power, I was just hauling Dodge Intrepid with it and I could not duplicate the misfiring while pulling the 6,000 lbs. trailer.
My ML made over 170K miles on the original sensors, heaters are still working on both of them when I test them with battery charger.
I'm not sure how many miles you have on your ML but if it is more then 100K miles, I'm sure it's time for new o2 sensors. Rears are just monitoring set after catalytic convertors and they should last a lot longer then front ones.
Trust me on this one, I ben there...
Bernard