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2005 E320 CDI engine misfire at idle when fully warm

688 Views 14 Replies 4 Participants Last post by  DieselBound
I have been pulling my hair out trying to solve this problem. Several months ago I noticed my car would sometimes stumble at idle after a long day of driving. It would only happen for a moment or two and it would smooth out. But as the weeks passed, the problem would happen more frequently with less driving, and eventually turned into a full blown misfire at idle. However the problem only happens at idle when the engine is FULLY warmed. If I let the car sit for a few hours and go to start it, the engine purs just fine....until it warms up again. And it only happens purely at idle and when I let my foot off the accelerator. Any throttle at all and the engine totally smooths out and works perfectly fine.

I have tried replacing the injector nozzles, seals, and return line o-rings with no change to the problem whatsoever. I just got done doing a leak off test and all the fuel levels were dead nuts even with each other.

I have replaced the fuel filter, bypassed the EGR valve, and I have all but deleted the swirl flaps. Nothing has even made a change.

I have taken this car to a mercedes shop to see if there were any hidden codes, and with the exception of the egr being bypassed, there are no codes for fuel pressure.

I honestly have no idea where to go from here. I would appreciate any insight you guys might have.
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How did you "bypass" the EGR valve?

Seems fairly predictable in which case this shouldn't take much to track down.
Correct, no DPF.

So... are you still witnessing the sounds up front when hitting 60C?

EGR functions are temperature-based. I don't know about the MB (I'm new), but I do know that my VW TDIs (ALH engines) deactivate the EGR valve around this temp.

Regarding the swirl flaps, manipulating them manually might have exercised them enough to free them up, a bit: I don't trust any of this stuff which is why I am installing a manifold w/o flaps (I can readily do this because I have my engine out). Intake flow patterns fluctuate as these flaps operate; supposedly they're supposed to be of most benefit at lower RPMs (likely to affect idle). I don't know if the ECU, in regards to triggering an error code, is able to fully track proper operation of the swirl flaps, whether it's a "it works or it doesn't" sort of thing vs a "it's only working x%".
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I'm OK with the EGR. I'd prefer to not have it but it's just too much of a hassle to do anything with it, mechanically speaking (my preference is to physically delete, but I decided to put all back together clean and go with it). The swirl flaps on the other hand... BMW ditched them because they realized that the pluses didn't outweigh the minuses. They were a good idea gone wrong. Little effect on emissions in which case I feel less nervous about this change: I fear a ramp-up in emissions testing for diesels as they're a target (I want to stay under the radar). I need to focus on doing a catch can: I think they have a more positive impact than about any other change.
US market did not get DPF until 2007 (om642).

That said, there's still the CAT, and while, in my limited knowledge, I'm not aware of anyone with this car having an issue with one, they can get plugged up (I know of such in the VW world).

Really have to have strong diagnostics to pin point. That or really establish methodical troubleshooting actions.
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