I've read multiple posts about this issue so i know I'm not alone, but i still dont feel any of them answer the problem, hopefully someone can help.

I have a 2005 C230 Kompressor sport sedan with 117,000 miles, about a year ago it started to misfire. Usually once id get into the higher RPMs (typically 4,500-6000) it would sputter, the CEL would come on, and id lose power, once id get back down to idle speed it would shake and shudder, misfiring. But as soon as i shut it off and turned it back on again it would run normal, then again it would start to misfire once i get into the higher RPMs or if I'm pulling from about 50mph in a higher gear (4th) around 2,000-3,500 RPMs. I read some of the forums on here and concluded a bottle of fuel injector cleaner would work, but it didnt. I then took it to our mechanic who told me he just had the same problem with another car like mine and had to do a valve job(which now i think i didnt need at all). So i did the valve job, problem was gone. Then about 6 months later IT RETURNED. I was getting ready to take back to my mechanic when bam, it was gone as quick as it came. This weekend i detailed my engine bay, covered all the vulnerable parts and used a gentle spray etc. etc. I let it dry for 5-6 hours then ran it, ran like a dream. I went out that night and on my way home, the same problem returned. I revisited all the forums again and today i took out one of the coils in cylinder 4, there was (what i assume to be) water there so i cleaned it out threw it back on and ran it, worked great till it heated to normal and started to misfire once i got it to about 6,000 RPM. Ill be taking off the rest of the coils tomorrow and checking for "water", hopefully that will work. A code reader would help a helluvalot but unfortunately i don't have access to one.

Needless to say any help at all would be absolutely great and much appreciated, I'm dying here.

If you have the same problem i do, chime in.

P.S. PCV hose has been changed along with the camshaft solenoids during the open campaigns

 

fixed it, pulled out the ignition coils and that port was filled with some type of liquid, maybe a mix of water & oil, couldn't tell, but i cleaned em all out let it dry, problem gone, i also threw a bottle of techron in there just to be safe.

 

Probably a stupid question but i don't think you mentioned if you replaced the spark plugs. Mine has the same mileage and I was getting spurious CEL lights that would clear after a day or so. I first thought that my wife may not have been tightening the gas cap when filling up, or that she wasn't turning the car off but after discussing these things with her it would continue to happen about once evey 2 weeks. I replaced the spark plugs and made sure to use dielectric grease on the end of the plugs where it mates with the coil and the issue is gone, the car feels way smoother and MPG improved a bit. One thing though, your coils should be making a good seal on the top so water should not be getting in there in the first place, if anything oil should but you just had a valve job done and any good mechanic should replace all those o-rings when they take the valve cover or head off. Good luck!

 

Yeah i did get the spark plugs changed when i got the valve job, but good point with the seals, ill look back into exactly what he changed in the next week or so, thanks.