W210Wagon

98 E320 4-Matic wagon. It started a month or so ago. I was getting on it fairly hard, trying to blend with freeway traffic. I ran it to about 4500 rpm. When I let off, I had a heavy miss. The miss would not go away. Drove to my destination. When I left there, no miss (hmm??). After that, the miss would come and go, but not consistent. About a week ago, it became constant. And sometimes it is worse than others. Sometimes a slight constant miss, occasionally a pretty heavy miss. Got my hands on a basic OBD II tool and got the following codes.

P0300 Random Miss
P0173 Fuel Trim (bank 2)
P0303 Cyl 3 missfire detected
P0305 Cyl 5 missfire detected
P0301 Cyl 1 missfire detected
P0170 Fuel Trim (bank 1)
P0130 O2 Circuit (bank 1, sensor 1)
P0100 Mass or Volume Air Flow Circuit

OK, so what does it all mean? Thanks in advance.

RichardM98

Sometimes codes cascade. That is, one code causes another which wouldn't have occurred by itself.

If you haven't done so, I suggest clearing all codes with your scanner, drive for a day or so and see what comes back.. Chances are the list will be smaller and more indicative of your problems.

W210Wagon

Alright. I will give that a try. Thanks.

W210Wagon

Latest development is that I cleared the codes. I started the car and before I could back out of my driveway, the check engine light came back on. I drove it about 20 miles. Some surface streets, some freeway. The car did seem to run better with the codes cleared. I checked it when I got home and only had one code. P0303. Miss on #3 cylinder.

RichardM98

Assuming no other codes reappear, you can check to see if the miss is due to the coil or the spark plug wires. Cylinder number 3 is the rear one on the passenger side of the engine. You'll need a torx bit (T30?) to remove the coil. To check exchange a coil from an adjacent cylinder with that one and check to see if the misfire moves to another cylinder. If not exchange the spark plug wires one at a time to see if it changes. Note - There is an A and B wire (clearly marked on the coil) so don't mix them up. Also, be careful to remove the wires carefullly from the spark plug. A 17mm open end wrench will just grip a ridge on the spark plug shroud and can be used to pry it off.

If not, replace the spark plug with an equivalent one. Read the DIY's on changing spark plugs for tools and procedures.

FYI - Based upon the codes you first listed my guess would have been the MAF or O2 sensor.

W210Wagon

I ran out of daylight to do a lot of testing today. Earlier in the day, I went by a pic-a-part wrecking yard and found a MB with it's coils. The price was so cheap, I bought 4 of the coils. First I checked the codes and still had only the P0303 code. I swapped the #3 coil. The miss was still there. It was getting dark but I did stick new plugs in the wires, grounded the plugs and started the car. I did have spark. By this time it was dark so I just buttoned things up.

RichardM98

A spark doesn't prove much since the high energy ignition would probably fire a piece of coat hanger in a cork.

The ECU uses information from all the sensors (MAF, CPS. O2) to determine the timing necessary. Anything slightly off and a misfire occurs.

W210Wagon

Updates. On #3 cylinder. Replaced the coil since I had a new one and just in case. When I pulled the plug wires, the "A" wire looked like it had not been working. Corroded looking wiring at the coil side. And the wire separated when I tried to pull it. "B" wire looked OK but I replaced both anyway. Both plugs looked kinda wet and nasty. Replaced both plugs. Good news. No miss. Car ran good and the check engine light cleared itself after about 3 starts. I drove it for a couple of days then I get another check engine light. New codes were:
P0300
P0303
P0170
P0173
I didn't notice any miss and the car still seemed to be running fine. Hmmm. I just cleared the codes and will check it again in a couple of days.

RichardM98

The combination of P0170 (or 1) and P0173 often indicates a failing MAF. A bad MAF will cause a over rich mixture which will over heat the Catalytic Convertor which will eventually fail.

W210Wagon

Thanks Richard. Is there a way to check that separately to isolate it and find out if that is what is happening?

RichardM98

The sensor is made by Bosch and I believe there is a test procedure although I recall it being too complicated for the average DIY. I think info on the sensor is listed in the W210 stickies on benzworld.

It's possible to try and clean the sensor. I clean mine with CRC MAF cleaner each time I change the air filter. But usually if it's gone far enough to cause a DTC cleaning doesn't work very well or for very long. To clean it the insert must be removed from the housing. If it's the original one, the insert is held on by two Torx 5 point (Torx Plus) security fasteners.

W210Wagon

It seemed like the screen had slight discoloration. Dirt? I did spray it with MAF spray cleaner but I didn't realize I needed to remove the insert. I might try that. I'll look for the test procedure for the MAF. Thanks.