I have a '01 ML320. Last week got in it, started it up. Immediately noticed rough idle, and slow to go with higher than normal RPMs. Place it in the shop. Spark plugs and their wires changed, one was bad. To my surprize I have 12 plugs and wires for a 6 cyl. I would have never guessed. But anyway it didn't fix my problem. I have a fuel filter ready to change out but the problem is I don't know where the fuel filter is located. The question here is " Is it my filter". I want my good running car back.
Your fuel filter has a built-in pressure regulator so it may indeed help your problem.
It's located just inside the left (driver's) side rear wheel.
You can probably see it if you shine a flashlight between the frame and the body just in front of the left (driver's) side rear wheel
If you remove the left rear wheel you should have enough access to replace it. It is tight though. Also, they (MB) did update the fuel filter on the earlier ML models which entailed replacing some of the fuel lines, so double check to make sure you have the " correct" filter.
The way you can do this is, after you get the left rear wheel off, see if you can read the numbers on the filter that's currently on there. You'll more than likey have to wipe the crud off it to it be able to read the number.