W164 ML320 CDI engine troubles - opinions wanted!

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New Member
Aug 6, 2013
BMW E92 330d + Merc W164 ML320CDI
Firstly, please excuse the long post, I have been having some engine troubles recently and I am hoping that the community can help me get to the bottom of it.

The car is a W164 ML320 CDI with the OM642 engine and about 133000 miles on the clock. The problems first started about a week ago on the way back from a 100 mile trip. The car went into limp home mode and the check engine light came on, a code scan revealed a turbo actuator fault. I purchased an aftermarket turbo actuator and fitted it without too many problems. In the process the air intake duct cracked where it meets the turbo.

Initially I put everything back together and planned to replace the duct, but wanted to see how the engine ran with the new actuator. Everything seemed fine at first, however after some time, particularly when the engine was warm it seems, it would log P0404 errors indicating an EGR function fault. I put this down to an air leak on the old intake duct and fitted an aftermarket replacement with new mass airflow sensors. I noted that there was definitely an audible air leak with the old duct fitted.

I fitted the new intake duct along with new sensors and confirmed that the air leak was gone. Unfortunately the EGR errors persisted particularly P0404 and P0401. In addition, now there is an audible coughing sound from the turbo as the revs drop between gear shifts along with very noticeable intermittent flat spots when accelerating. To be clear there were no errors or strange sounds before this entire episode started.

This is the point I am at at the moment. It seems unlikely to me that a whole host of components all failed at once, however every component I have replaced has not addressed the EGR errors. I have not yet removed the EGR but plan to do so. As a replacement part it is very expensive so I am not particularly eager to buy one on the off chance. The other possibility that occurs to me is that the aftermarket turbo actuator that I purchased is not behaving per the original spec but I'm not sure whether this could cause the EGR errors I am seeing. I have definitely confirmed that the turbo actuator is moving as I can see it when I rev the engine, also when it was off I confirmed that the lever on the turbo housing moves freely without catching.

Any advice or experience from the community would be welcomed as at the moment I am coming up blank.

Thanks in advance

Hi all,

So I ended up replacing the EGR as a local garage told me that it was shorted on the electrical side. Sure enough the EGR errors are now gone, but the coughing and flat spots are still very much there.

I think I have ruled out an intake air leak, and the mass airflow sensors were new with the intake, so not sure where to go with this next.

Any ideas very welcome at this stage!


When you fit new air mass sensors you have to use the diag to tell the ecu that you’ve replaced them.

Not sure that’s the fault but you’ll need to try it.

I would suspect the actuator is the issue but difficult to tell through posts.

You should be able to get the actuator position on live data and see if it goes wild when it coughs.

Also the back pressure sensor can go faulty and cause similar symptoms that you describe, again usually has a fault code but will have live data you can check the reading.
Thanks, that's exactly the sort of detail I was looking for.

Was looking at Autel diags as at the moment I'm just using a Bluetooth adapter and an app on my phone and I'm not getting the live data I need to diagnose this one. Also no option to recode the ECU for the new MAF sensors.

Would the Autel MD 808 be overkill or about right?
Is there anyway to patch up your old intake just to rule out the replacement MAF’s? Was the new pipe a genuine MB part as pattern MAF’s can be an issue.
The old intake was beyond patching so I threw it out, but I did keep the original MAFs. Yes the new ones were pattern and came with the new pattern intake. I could easily swap out the new MAFs for the old ones.

The other thing is that this morning I tried sticking my phone under the bonnet and doing a video of me revving the motor, I could see some small puffs out of the intake from near where it mounts to the turbo. I suspect maybe that it's not on there as well as it should be which presumably would cause all sorts of issues.

I think I need to:

- Swap out the MAFs for the old, working ones
- Remount the intake taking extra care to make sure its on the turbo good and tight
Also I looked to see the position of the actuator when revving the engine, not sure what it should be doing exactly, but didn't look too crazy. The coughs didn't seem coincide with the actuator moving though.

Video here, where you can just about make out the puffs of smoke: New video by George
Couldn’t really see from your video, almost looks like some fluid burning off. The intake is generally under suction so puffs of smoke will come from the pressure side. The o ring at the outlet of the turbo between the solid pipe running forward goes. You can usually see some evidence of gas escape or look closely at this area when blipping the throttle. It is a faff to change and easily damaged or not seated correctly that causes the problem. There is a o ring at each end of the pipe. Get a new one of each. Depending how tight access is you should just have to loosen the bolts holding the resonator on which will give you enough wiggle room to get the pipe off. There is a little clamp at the resonator end and it just pushes over the turbo outlet. There will be a bolt holding the pipe to the cylinder head.
Hi Andrew. Thanks, but not sure it's fluid burning off, as there are visible puffs as the revs drop. Feels like it's when the EGR opens and puts stinky exhaust gases into the inlet manifold but I could be wrong. Definitely looks like it's coming from the union between the turbo and the plastic inlet duct.

I'll try to get a better video later, at the moment looks like the heavens are going to open :-|

Really appreciate all the support guys :)
Quick update, I just reseated the plastic inlet pipework paying lots of attention to each joint, and refitted the original MAFs. The little puffs of smoke etc that I noticed before are gone and the pickup is far better without the severe flat spots. I'm sure there's a better seal between the inlet Y pipe and the turbo.

Unfortunately the coughing when coming off-boost is still there, so I'm now pretty sure the (suspiciously cheap) aftermarket actuator is at fault. I've just bought a remanufactured one (original Hella item) which should be here in the next few days, so I'll fit that and see where that leaves me.

Will update the thread either way so that anyone coming here after can benefit from my experience anyway.
I forgot to update the thread but I did get to the bottom of the problem and resolve it. Here's what happened for anyone that comes across this with similar problems in future.

The issues appear to have been caused by the non-oem turbo actuator that I foolishly bought and installed in a hurry to try and get the car going in time for a holiday trip.

It seems the aftermarket actuator was not reacting correctly and I think overboosting when the revs were dropping, causing the car to drive terribly.

I ended up replacing that with an OEM unit that had been remanufactured by Turbo Vanes, after which the problem was solved.

Turns out I also have an iffy O2 sensor so need to sort that out but the engine / boost / EGR issues are at least sorted.

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