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Hello MBW...I hate for my first post to be an issue, but here I am. I'm generally active on a broad spectrum of forums, so I'll be around. Working on my daughters '12 C250 with around 130k miles, I am the second owner, had dealer service its entire life. Ran flawless but the oil filter housing had a bad leak.
Issue: removed the intake manifold to replace the leaking oil filter housing (replaced the starter as recommended from the oil soak). Replaced intake gaskets and reassembled. Test drive was good, though in retrospect I did notice a very slight and random misfire at light throttle cruising. Battery was disconnected for a few days so assumed it might be fuel trims getting back in line. Next day, daughter reports MIL is lit and a scan reveals misfires on 2-4 cylinders and a random misfire code (P03xx I think they were). I did something I don't normally do and threw parts at it, in this case coils and plugs. Test drive reveals a beautiful idle, but light throttle it bucks and stumbles slightly. Give it the beans and its fine. Previous codes have returned/still present.
I'm convinced it's something I did and plan to disassemble to review, but would the intake actuator (not even sure what it does) have anything to do with this stumble that is manifesting as a misfire? I took it off to better reach the manifold bolts at the back of the engine), but not sure I have it aligned/installed properly. Lastly, what is the preferred portal for accessing the FSM? I use Alldata for my other cars, but this is my first MB. Thanks in advance.
Could be an air leak somewhere. Check all the gaskets, was the intake manifold torqued down properly, all hoses reconnected and not damaged? Im not personally familiar with the M271 so not sure what it looks like in there.
OK, finally stopped raining so I can get back to this. The misfire codes are below. I'm not sure why I would get misfire codes if there is unmetered air, seems like that would present in a lean bank code. Going to check my work, the MAP/MAF sensors, and see if this actuator has anything to do with it. Odd that cyl 1 has never had a misfire during this episode.
P0300 (random misfire), P0302 (cyl 2), P0303 (cyl 3), and P0304 (you guessed it, cyl 4).
Closing the loop on this, it was in fact the intake actuator that was 90* out of phase. It's a motor that connects to some sort of intake track flapper valve with a square drive and it can connect in two different positions. When I took it off this morning I realized it wasn't in the same position as the first time it was removed. All back together and it drives like new and no codes after three drive cycles. It was putting up codes immediately before, so feeling good its resolved.
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