mfotovati

My car is 2003 c230 with about 90k .My engine light came on and the car started idling roughly. I checked the codes and it reported a p-0302 (cylinder 2 misfire). Restarting the car cleared the rough idle, with the CEL still on (occasionally it will go through a drive cycle and clear the CEL, but only every once in awhile). So far I changed all four spark plugs . I swapped the coils between cylinder 2 and 3 to see if the problem followed the coil, it did not. I replaced the fuel filter (thought maybe the #2 injector was more sensitive then the others.)
I did this work over the course of the past two months, and the only code that was logged was The p-0302. This code was only logged at idle (the misfire never occurs under high rpm's/loads) and more prevalent after being on the highway and coming to a stop at a light shortly after exiting.I saw other people complain the same thing with the same car but I never heard what is happening finally to fix the issue .could you please let me know what is the problem ,(sensor ,fule injector ….)
Thanks

Ausmbtech

I'm presuming you have a M271 engine (black engine covers)

You probably have a sticky exhaust valve which leads to a momentary loss of compression in that cylinder.

There are modified (tighter) exhaust valve springs, modified engine software and modified exhaust valves.

I'd try driving the car in low gear above 4000rpm (MB directive to help clean valves) at high load if possible for about 10mins. Then use a can of Subaru upper engine cleaner while holding the revs at approx 1500rpm.

Clear the CEL then drive normally for about 10 mins.

If fault clears then try and get the modifed software installed from your dealer, this will help prevent the fault from returning.

mfotovati

Thanks for your information.
I am going to show my car to dealer .Are they going to replace this stuff with modify one as you mentioned or just clean it and leave it.I also heard that cylender head has some kind of problem and new one is modified .Here in Canada we have warranty for 5 years 120000 km .my car still is under warranry for few more months.one thing that make me worry is if they just temporary fix the issue does it back again or this modify replacment is final answer becasue i want to keep the car .I will ask dealer kindly to replace these stuff hope they listen .Do you have any advice before I booked my car for this problem.

Ausmbtech

just the new software seems and a carbon clean seems to work on most cars, only the worst ones really need the modifed springs these days.

mfotovati

Thanks ,I will keep you posted what is happening.

mfotovati

Problem fixed by dealer:
Replaced cylender head , valve ,spring . Thanks guys