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Author: Subject: Tintop help: BMW diesel running rough at idle/low revs (over-fuelling)

posted on 29/10/18 at 09:42 AM Reply With Quote
Tintop help: BMW diesel running rough at idle/low revs (over-fuelling)

Hi guys,

I wonder if there's anyone out there that might have a bit of knowledge when it comes to troubleshooting diesels...

The car is:
- 2005 BMW 120D E87
- M47 diesel engine

The car started belching out dark grey smoke when under load on throttle and progressively got worse. It now runs really rough (like a misfire) at idle up to about 2500rpm after which it suddenly switches over to running OK.

The biggest clue I have (I think) is that when idling if you pull the plug off the MAF sensor it goes from stuttering and smoking to suddenly running absolutely fine.

I hoped it would be as simple as changing the MAF sensor so I bought one off an eBay supplier, supposedly a genuine Bosch - came in a Bosch box with a authenticity seal that checks out OK on the Bosch website. Sadly changing this over hasn't made any difference.

I've also taken the EGR valve off and cleaned all the carbon cr@p out of that. Put that back on and run it but no change. One thing I did notice when looking inside the EGR valve again was that it was dripping wet with diesel only after a minute or two of engine running.

I've got an OBD cable and installed the BMW diagnostic software ISTA+ on my laptop but that's about as far as I've got because if I'm honest I'm sure what to look at next to try and diagnose this.

Anyone got any ideas?


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posted on 29/10/18 at 10:33 AM Reply With Quote
Advising I've had a couple of relatives suffer with diesel exhaust DPFs recently is all I can advise.

Sister on a Ford SMax - went to the local Ford dealer a couple of times and they simply failed to resolve the issue. A pretty good motorway session with her husband made it bellow black smoke for a few miles, but seemed to resolve the issue. After that they'd pretty much lost faith in it though and replaced it with and ovloV XC60 (diesel).

Father with a Jaguar F Pace. Went to the deal (under warranty) and the dealer seemed to sort it in a couple of hours. It's been fine for the past 4 months.

Your car being 2005 it may not even have a DPF in the exhaust of course so that may have nothing to do with it.

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posted on 29/10/18 at 11:04 AM Reply With Quote
As you say it could be a dpf I had issues with a 2006 5 series 520d years ago.

Similar symptoms to yours.

The egr valve was a mess I cleaned it and no better
I removed the dpf and replaced with a new one still no better.
Did not remove the maf so not sure if that would have stopped it
Went to a bmw dealer in Morley Leeds and they replaced the egr valve. Even though I'd cleaned it and it was OK.

My car had done 230k on 1 dpf filter.

One mistake was not driving it hard occasionally as the regen process did not work after about 210k miles.

Good luck.



David Johnson

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posted on 29/10/18 at 03:49 PM Reply With Quote
A 2005 120D shouldn't have a DPF on it, they were fitted from 2007 on.

If the MAF is ok then it could be a failing (leaky) injector.

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Angel Acevedo

posted on 29/10/18 at 04:03 PM Reply With Quote
Or MAF wiring?

Beware of what you wish.. for it may come true....

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posted on 29/10/18 at 04:05 PM Reply With Quote
Forget to mention a local diesel specialist tested the injectors and reported they were OK. I don't know what else they did if anything or what conclusion they came to as I wasn't there when the work was carried out. I've taken on this car to help out a friend who's at their wit's end with it.

There's a niggling voice in my mind that the new MAF may not be doing what it should either just because eBay is notoriously full of unscrupulous types who are quite good at dressing up copies as genuine. I have a feeling that someone in the know would be able to use ISTA+ to determine that the MAF is operating within expected parameters (or not) but to me the numbers mean nothing at present.

I'm also aware that there may be nothing wrong with either MAF and that disconnecting it puts the ECU into safe mode, masking another faulty sensor. If that's the case I don't know where to starting looking.

The last time I cleared the fault codes and re-run the car the fault reports looked like the attached pic. I suspect the heated fuel filter error is another red herring caused by something else going wrong.

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