[ss335i]

Hello Everyone, if anyone can please enlighten me as I am somewhat of a noob when it comes to N54's. I have a 2008 335xi E90. The car has gone into limp mode many times, which drives me up a wall as all my friends call me "captian limp" experienced a misfire for the first time 2 weeks back. After the car misfired, I let it sit, and Drove it back home at 45mph and under. after driving it like that the check engine light goes away and the car drives normal. The next day I go and scan the vehicle which read "misfire on cylinder 4." I was later instructed to get sparkplugs. In the mean time, the car runs good, only went into limp mode a few times but no check engine light. fast forward to now, Just got the plugs (OEM BMW plugs, I am not tuned im only running a muffler delete.) and have not installed them yet. I start my car after work yesterday and let the vehicle idle as I didn't start it for 7 hours since I turned it off after my lunch break, which also drove fine with no idiot light and no limp mode. After letting the vehicle idle the RPMs were constant at around 6grand RPM's and the the RPM's started bogging out and went down to 3500RPM's almost as if the motor was gonna shut itself off. And like I said I am a noob but that seems like a misfire at idle to me. Drove the car after the fact, no limp mode, no idiot light. Look I know this is turning into a novel named "Help my BMW" but the real question to this is, Will sparkplugs solve all of this nonsense? or would I have to get more parts. I wanted to explain all of this in detail so I can give you guys the most imput. Thank you.

[Oolien]

if your plugs are shot then yea that would cause a misfire, also check your coils

[robthewrench]

If you do some searching for common N54 issues you'll find that misfires are very common. The N54 has two designs that aren't great: 1) The injector design is proprietary to BMW and thus replacement injectors are expensive and sometimes not reliable. 2) The N54 PCV / oil separator is not great and this leads to more oil in the combustion air, so fouling of plugs, build up of carbon in the intake track.

You're on the right path by scanning for codes, but to answer your question, no it may not be limited only to spark plugs. You may end up at some point also having a problem with coils / injectors and also an intake walnut blast. I'm not sure if you read the mis-fire code with a standard multi-car OBD diagnostic tool or a BMW specific tool. Do yourself a favor and get a BMW specific reader set up. It can be just a cable and laptop with some free software. Reading the BMW specific codes will be way more helpful than only seeing the emission OBD codes.

[tcphoto]

After chasing lean codes and misfires on my E46, I found that if your plugs aren't fouled odds are it's a coil or vacuum leak. I've been in my E92 for nearly three years and have only needed one coil...knock on wood. I would consider doing a walnut blast if you haven't already and take a look at the plugs for oil. I find that Carly for BMW is a good place to start diagnosing problems.