[Salzamani]

Originally Posted by Dann

No-one is going to read that, far too wordy and long.

Use some paragraphs ffs.

I read it word for word and couldn’t believe how accurately he discribed the issue. I have experienced the exact same thing. I fortunately still had the original BMW spark plugs that came with the vehicle and even though they have 65k miles on them once they were reinstalled the rough idle issue is instantly gone. I think it must be related to the vehicle getting use to the larger gap as the spark plugs age/wear. I’m going to continue leaving these original plugs in the vehicle another week to confirm and then as a final experiment gap the new spark plugs to match the original old plugs and reinstall them to see if it was truely just the gap that was causing the issue...

[Salzamani]

Here is my update. After leaving the original 65k BMW branded spark plugs in the vehicle for a full week and noticing that the idle was perfect I decided to go ahead and as a final experiment reinstall the new plugs to see how the vehicle ran and once again after warm up there was the rough idle followed by the annoying idle increase to help correct the rough idle. So now it came down to the spark plug gap as the most likely culprit. so I pulled out the new plugs once again and gapped them to match the old 65k spark plugs .035in/.889mm and reinstalled them once again and to my surprise rough idle/fluctuating idle was gone. Whoohoo! It was the gap on the plugs after all. These BMW branded plugs and Bosch brand plugs both come pre-gapped out of the box pretty tight and I’m sure it is fine for some N54 engines but for whatever reason my N54 engine does not like that tight of a gap. To gap them I just used a very small needle nose pliers and just pulled slightly to widen the gap of each of the 3 prongs and made sure they were about .035in/.889mm it’s possible that I might have not really needed to gap them that big but as I mentioned before that is what the old plugs were worn down to so I just tried to keep them the same. I may try NGK plugs in the future...

It is also very possible that the stock tight gap could work just fine if one has access to the above mentioned methods to rest some settings but for all those who have tried that with no success give opening the gap of the plugs a try. There is no other explanation as to why putting back the old plugs solves the issue instantly.... hope this helps someone else out there. If you have any question feel free to message me 👍🏼

[iseck1]

Originally Posted by Salzamani

Here is my update. After leaving the original 65k BMW branded spark plugs in the vehicle for a full week and noticing that the idle was perfect I decided to go ahead and as a final experiment reinstall the new plugs to see how the vehicle ran and once again after warm up there was the rough idle followed by the annoying idle increase to help correct the rough idle. So now it came down to the spark plug gap as the most likely culprit. so I pulled out the new plugs once again and gapped them to match the old 65k spark plugs .035in/.889mm and reinstalled them once again and to my surprise rough idle/fluctuating idle was gone. Whoohoo! It was the gap on the plugs after all. These BMW branded plugs and Bosch brand plugs both come pre-gapped out of the box pretty tight and I’m sure it is fine for some N54 engines but for whatever reason my N54 engine does not like that tight of a gap. To gap them I just used a very small needle nose pliers and just pulled slightly to widen the gap of each of the 3 prongs and made sure they were about .035in/.889mm it’s possible that I might have not really needed to gap them that big but as I mentioned before that is what the old plugs were worn down to so I just tried to keep them the same. I may try NGK plugs in the future...

It is also very possible that the stock tight gap could work just fine if one has access to the above mentioned methods to rest some settings but for all those who have tried that with no success give opening the gap of the plugs a try. There is no other explanation as to why putting back the old plugs solves the issue instantly.... hope this helps someone else out there. If you have any question feel free to message me 👍🏼

Great work confirming the gaping of the new plugs works. I never got around to it yet as as I got busy with other stuff. I can however confirm that I did reset the adaptations with the bad plugs and it did not make a difference to me. From what I can gather the smaller gap simply does not make a big enough spark given the cylinder conditions to prevent misfires. There is probably some science to the smallest and largest gap possible for the system to adapt after which misfires start to happen. Since the plugs come pre-gapped that's likely why there is not much discussion on it.

[Salzamani]

Originally Posted by iseck1

Great work confirming the gaping of the new plugs works. I never got around to it yet as as I got busy with other stuff. I can however confirm that I did reset the adaptations with the bad plugs and it did not make a difference to me. From what I can gather the smaller gap simply does not make a big enough spark given the cylinder conditions to prevent misfires. There is probably some science to the smallest and largest gap possible for the system to adapt after which misfires start to happen. Since the plugs come pre-gapped that's likely why there is not much discussion on it.

What was the procedure you used to reset the adaptations? Did you follow Mr 5’s guide?

https://www.e90post.com/forums/showthread.php?t=386376

[JMC54]

Originally Posted by Salzamani

What was the procedure you used to reset the adaptations? Did you follow Mr 5’s guide?

https://www.e90post.com/forums/showthread.php?t=386376

Hi All,

I am a newbie to Bimmerpost, and this is my first post. I purchase a 2007 N53 E93 325i convertible last month - took it to the garage to replace the spark plugs and since then its been in 3 times. Rough idle and engine check light. The error code states coils but the garage have checked them twice, and there is no problem. Sound like a similar problem to the above posts. Original spark plugs where NGK the first replacement where bosch, second replacement where bosch and the last set were NGK. Starting to pull my hair out. On each change, the car ran fine for a few hours then rough idle and engine warning light back. Can any recommend a garage in London who they have used for a similar issue? Thanks

[Chap0e92]

I have a p0440 code, 60k miles and every time i start the car it revs up by itself to like 2' rpm for like 5 seconds and goes back down to normal, just started doing it too... any suggestions?