Hi guys,

I've been experiencing a very odd (and annoying) idling behavior, when I select "D" on my 2012 SD4 auto. I've searched quite a bit, but mostly got posts relating to rough idle, which seems to be a slightly different symptom.

In my case, when I select D with the brake all the way in, sitting at a stop sign or traffic - the RPMs drop from about 800 to 600, feeling as if the engine is just about to stall for a second or so. Often this dip happens once every 4-5 seconds for a couple of times.



I was able to plug in my Autel reader, and took a screenshot of the MAF sensor, which shows slight bumps in air getting sucked in, from 6 to 8 even 10 g/s when this occurs. But this could be just a reflection of the rpms getting back up causing more air to be pulled.



I don't have any solid leads yet... Any advice on how to approach something like this, or any similar accounts would be appreciated. TIA FL2 engineers!

I seem to recall replacing the intercooler hoses fixing this for me - would pull up to a stop sign/traffic lights and the revs would dip and jump to the point I thought it would stall. Got progressively worse as the small split in the hose got bigger. Worth a look.

Awkward job to get them both off, nothing hard, just fiddly. Best to take the front bumper off.

Assuming the intact tract is OK, as mentioned in the above post, any modification of the MAF values, when idling, without pressing the gas pedal, is because of the EGR which is allowing exhaust gases to pass or not.
This behavior is normal up to a point, because the ECU is trying to fine tune the EGR, by compensating for the effects of wear and tear and carbon deposits on the intake tract, during time.
Mine does it too, but not so obvious, mostly after startup, during warmup time, for a few minutes.
Try cleaning the EGR first, if you don't want to permanently disable the EGR, which will solve the issue for good.

Thanks for the pointers!
I'd rather keep the EGR only because of the DPF, which also has to be disabled in that case.

It definitely looks like a compensation mechanism kicking in... Originally I suspected faulty sensor somewhere sending incorrect values, or fuel pump / injector issue. But intake pipes losing pressure or EGR makes a lot of sense.

Do you think it would be possible to observe this through the live data from some EGR sensor? Such as the EGR position sensor, or % bypass, something along those lines?

Also, how difficult is to take out the EGR and clean in a DIY setting?

Thanks!

Had a similar problem a while ago. Discovered the air filter cover screws were a bit loose and the cover was therefore leaking a bit. Tightened screws and problem disappeared. Coincidence or not the problem resolved itself so might be worth checking for obvious leaks in this area

I'd really have a second look at the MAF sensor and airbox first.

Small update here.
Intake piping/filter box seem to be ok.
However, the issue is still persisting if not getting worse. So I started looking at the EGR valve opening values in realtime when this occurs, and not unexpectedly we can observe these large dips in the EGR reading exactly each 4 seconds when the rpms dip... What gives? To start with, I'll do an EGR cleanup first, and hopefully some feedback from that.


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PS. Of course it's also possible that the EGR dips are a response from the ECU when the RPM's dip

Thread revival! Kasapoff did you find a solution? Any advice would be good, similar issue on my SD4, but no access to diagnostics for more info.
Thanks.

Unfortunately no resolution (or diagnosis for that matter) so far.
I'll likely resort to bringing it to the local LR dealership, at least to see if they can diagnose. Seems to be getting worse if driven less by the way.

Thanks for the reply kasapoff, I will chat to my specialist about it. If they find a resolution, will let you know.

Update: I was looking into the gearbox as a possible culprit, and did a software update at the dealer. So far it looks like a significant improvement of shifting, but didn't solve the issue with the idle. I was hoping that it's a software issue related to the auto-neutral function, but doesn't look like it so far.

How would you describe your symptoms Thrud? Were there any updates?

No updates yet really, reset gearbox using start button method and am running Hydra Maximus fuel system cleaner through the car for a few thousand miles though. Seems slightly better after a good run towing the caravan and no major recurrence so far. When it goes in for a service in July/August I will chat to them about it as well. Sorry no definitive answer....yet!

Thanks Thrud!
I'm confident we'll get to the bottom of it.

I do have one update. Based on the following thought process, I was able to rule out an issue with the transmission with a fairly high degree of certainty.

1. Connected the AP200 and found a "neutral control" on/off parameter in the TCM control module.
2. Start the engine and observe the realtime status of the auto-neutral feature (disconnects the transmission from the engine, much like when N is selected, but automatically after about 5 seconds of pressing the brake pedal at a stop light).
3. When the "hiccups" started I was looking at the neutral control function, and found that the engine only drops the RPMs if the function is off (meaning some light engine load while idling).
4. Once the function is on - the engine goes back to normal idle.

Based on this, we can rule out the auto-neutral function as a culprit, and focus on the engine. (eg: EGR, intake air, or fuel delivery). Also, the fact that it happens every 4-5 seconds regularly does appear to be unconnected to the transmission.

Hopefully this makes sense an is helpful. Will keep posting my findings. Good luck!

Thanks Kasapoff, I think (guess...) my money is on the egr. Glad you feel it is not the 'box will update when I have more info.

Finally resolved - as suggested by Alex and Thrud, it was the EGR. Mapped it out at an indy shop few days ago, so far happy with the outcome. No more dreaded hesitation, better throttle response at low rpms, overall tighter feel of the engine. Good luck to anyone with similar symptoms, hope this helps.