[928]

My 2010 335 xdrive sedan (completely stock) has had a mildly rough cold idle for several months. I see a number of posts about similar issues but the symptoms for those folks seem to be more severe. So, I thought I'd post my specific case in the hope of getting some guidance (unfortunately it looks like many here have had fuel-related issues and so have expertise).

The idle is rough only on cold start and it's only noticeable when it kicks down from the high idle to it's normal idle. I always wait for the car to kick down to normal idle before putting it in reverse and backing out of the garage. So it idles a bit rough as I back out but by the time I've closed the garage door and am driving off it's no longer rough.

I've been leaning toward injectors being the issue since they are original (the car has only 50,000 miles) and the symptoms certainly appear consistent with leaking injectors. The HPFP was replaced under the recall several years ago. A few months ago I replaced the plugs and the coils and that did not help. I read the codes (with Bavarian Technic) and it showed misfires (see the snip below with the misfire codes). I cleared the codes and started it up and it ran quite rough. I turned the car off and restarted and it ran normally again. It was as though the car had adapted and clearing the codes made it unadapt and run really rough. At that point I took it to the dealer for diagnosis. However, I had cleared the codes and they weren't sure if all codes had come back. But they said their computer was pointing to the injectors as the cause. I decided to monitor given the high cost of injectors. I checked the codes periodically since and didn't see any engine codes, though the same mild rough idle persisted.

I drove it yesterday, let it sit overnight, and then pulled the plugs today. I was expecting to see fuel on one or more of the plugs. Two of the plugs (corresponding to cylinders 2 and 3) had what appeared to be oil around the top of the threads, but the the rest of the threads and the electrode were dry. No smell of fuel at all. I'm attaching pictures of the plugs for each cylinder below.

I then read the codes with my Bavarian Technic. I'm attaching a snip from that as well. No misfire codes this time but instead 29DC and 29F2 (fuel related).

As the injectors and HPFP are both very expensive, I'd like to be as sure as possible that one or the other is the problem before replacing them. There is no delayed start and the car runs great.

Before I bite the bullet and spend the $$ on new injectors, any and all input regarding what is the most likely source of the issue is most welcome.

[928]

I can see how this might be a tough call. I guess the best question is, if it were your car and your money, how would you proceed? Would you change the injectors? Hold off and keep monitoring to see if the symptoms get worse?

[ragingpanda]

If it was my car, I would personally replace all of the injectors and hpfp for peace of mind. The way I see it on this platform is that they are maintenence items that need to be addressed. It would be far easier to diagnose if you had mhd for logging capabilities. If it really turns out to be leaking injectors which is a known problem with this platform (12 revisions), the fuel will thin out the oil and potentially cause spun bearings and a lot more $$$ in the long run.

[TunafishE93]

I would change those plugs with single electrode, easier to gap properly.. On that note from the pics which are kinda hard to see, it looks like the ground electrode is too close to the centre electrode, what's your gap on those?

29D9 service notes-Refuel, ignition coils, spark plugs, ignition cables, injectors, DME

I would not mess with injectors.. Your only injector code is not active.. Your active codes points to miss fires (plugs/coils).

What coils did you replace with?

[Meeni]

Pictures of plugs show 1/3 very white and 2/4 somewhat white which does support running lean. Now since you have at least 4 cylinders running lean Id' take a look at fuel pressure before going to replace any injector. Definitely diagnose before throwing parts at it.

[928]

Thanks for all of your replies. The guidance really helps! Your comments remind me that I first noticed the rough cold idle some time after I replaced the plugs (replaced as routine maintenance based on time). I still have them so I'll put them back in. I replaced the coils for cylinders 1 and 2 after I saw codes for misfires, so I can put the originals back in for those as well. I'll drive around a bit and see if that makes a difference. Regarding logging, I have a Bavarian Technic Enthusiast so I think I should be able to log fuel pressures, so will check into that as well. I'll report back once I have data.

[928]

I don't want to jinx it, but it appears that TunafishE93 was bang on! I replaced the plugs and coils with originals and it would appear that the problem is gone. Funny thing is, when I took it to the dealer I told them I had changed the plugs with Bosch aftermarket and asked if that could be the problem and they said no. I also asked if I needed to reset any adaptations relating to plugs and they said no. Below is a pic of the original and aftermarket plugs. The gap on the original is much wider. I've read that these 3 prong plugs come with the correct gap and are not able to be gapped. Is it possible to gap them or should I just buy some new replacements (from the dealer this time)?

[TunafishE93]

You can gap them.. Specs are .027 inch.

I bought Bosch plugs (single post) that were suppose to be factory gap. I had a range from .038 to .018 in six plugs.. So yeah I would always check.

[928]

Ok, I'll give that a go next time I'm in there. Thanks again for you help!