I got my dream car - 2001 E55 with 150k miles in September 2020. It was purchased new from a dealer in SoCal and was serviced there it's whole life. I am basically the 3rd owner and 2nd owner had it a year - he has a bunch of Mercedes including a W211 E55 and decided to part ways with this and some of his other cars to simplify his life. He told me the MB dealership informed him it needed new valve cover gaskets and that if he were me he would do the spark plugs then too because there was no indication of when they were last done if at all (he did oil, transmission fluid, tires during his approx. 1 year of ownership).

I drove the car a few months before undertaking the work and after reading in these forums, watching YouTube videos and ordering a spark plug change kit (including instructional video from MercedesSource) I got to work on it (with very limited previous experience). I found some damage on the valve covers and was advised to replace them so I did with used ones that I cleaned up thoroughly, replaced both valve cover gaskets with genuine Mercedes ones, resealed breather covers with MB gasket maker, replaced all the spark plugs with Bosch Dual Platinum ones, replaced the four breather hoses (OEM), replaced the air distribution hose connector, cleaned the throttle bottle (CRC Throttle Body Cleaner), cleaned the MAF sensor (CRC MAF cleaner), replaced the engine air filters (Mann) and put it all back together. I started it and it ran pretty rough but no check engine light. I realized I didn't have the air distribution hose connector pushed into where it should be so did that and the car ran a lot better.

I drove it maybe 10 times and noticed that sometimes when I stop at a traffic light it ran a bit rough (it did this before too) but then I got a check engine light and it started running really rough whenever I slowed or stopped in traffic. I plugged in my very basic code reader and got P0300, P0301, and P0304 and also 3 pending (P0115, P0130, and P0150). I also have noticed a very slow drip of what I think is oil (it is just a drop or two a week really) under the engine on my garage floor.

I checked all the breather lines and they seem fine, I refitted the MAF (it seemed fine) and then I removed the spark plugs from the first cylinder to look at them and make sure they were seated properly. No change. I was surprised at the condition of the spark plugs with less than 100 miles on them but maybe they are totally normal (I'm don't have any frame of reference other than what they looked like new). I'm attaching a pic - note that I used a dab of nickle anti-seize compound on spark plug threads when I initially installed them per MercedesSource instructions but have later heard this is a controversial technique) - maybe the black stuff is just the anti-seize not sure if it's a problem.

Anyone have any ideas for me? I don't know what to do next but I'm happy to try any suggestions within my skill set. I searched online and saw that the p0300 codes are about cylinder misfire in 1 and 4 but also saw that with the other codes it could be something else like MAF. I guess it's possible I broke the MAF while taking it out and cleaning it but I don't want to spend the money on a MAF and find it is not the problem if there is something else I should be doing first.

I assume unrelated and this can be fixed at a later date but in case relevant (pardon my ignorance) my windshield washer fluid is not spraying (I get no power at the pump when checked with volt meter and sprayer is engaged and have checked all the fuses with a volt meter and they are fine) and I believe the same with my headlamp washers but other features on car seem to be working.

Thank you in advance for any help or suggestions you might be able to provide.

 

could be a vacuum leak, or fuel issue when car is at idle speed.

try changing the fuel filter or fuel pump (its under the car just beside the rear driver side tire).

Chasing vacuum leaks can be tough, it could be a brittle hose that connects underneath the throttle body by the secondary air pump.

 

Thank you for these suggestions! I will research vacuum lines a bit to understand them and then see if hoses look ok or not. Also, is there a way to test fuel pump or is only option to replace it and see if that fixes the issue?

 

there's a Schrader valve located on the fuel line on the corner of the passenger side cylinder bank. it look similar to the plugs you have on your tires to fill air from.

You will need a special pressure gauge that you can screw onto it to read the fuel pressure.

if you have leaky valve cover gaskets thats also a spot to find vacuum leaks, or even a loose oil fill cap too.

 

I had a problem with collapsing vacuum hose at idle. I bought cheap ones and they lasted a couple of months until rough idle stated. Pulled the air cleaner and there was the collapsed VC

 

Thanks for your reply but unfortunately I'm not following. Is the air cleaner the box on top of the engine with the air filters in it? Also, what's a VC? Thanks!

 

Sorry. There is a black vacuum hose under the air filter box attached to the tops of Valve Cover
Oil vent pipes in the photo. Check them for cracks or collapse.

 

Oh yes, the breather hoses - I replaced those about a month ago with OEM ones as part of the valve cover gasket job. So, unfortunately I don't think that's my problem. Too bad, that's a nice easy fix lol.

 

Did you ever figure out what it was? I'm having the same issue.

​​​​​​Thanks!

 

Could be coil pack.