Agh, where to start…
2014 Td4, 86k - bought this time last year and it’s been a busy one*

Last week I got a P0405 code for a faulty EGR valve sensor position, decided to buy a replacement valve and swap it over. Whilst it was quite a learning experience, fair to say I wont be doing it again in a hurry.

Upon startup, there was no error code, but it was idling rough, ran okay when warm, a little hesitation when accelerating on the lower rev range. I diagnosed this as a potential faulty MAF as disconnecting it seemed to solve the issue.

Changed over the MAF (and MAP for good measure) and it still has a rough idle, especially when starting from cold. Driving it feels okay at higher speeds and revs, the turbo is definitely kicking in etc.

I’ve read murmurs online about requiring a recalibration of the air path, is there any truth to this, or do I likely just have a dud part? The mechanic I know seems to think the ECU should “learn” the new valve after a period of driving.

I should mention I managed to get a better scanner look at it today with a ‘live view’ of the EGR duty. The trace was pretty jumpy, even when idling. It went through periods of 16-20% duty when idling - though I understand it should probably be closed when idling (0%) and increasing when revving. It did seem to increase when the revs were increased.

Other symptoms include a strong smell from the exhaust, all pointing to a bad air/fuel mix - albeit with no error codes.

Just to preempt any suggestions, I have checked the following:
- turbo/inlet hoses are all intact
- all gaskets to/from the EGR are seated correctly and there are no leaks in the air intake.
- changed fuel filter as part of its annual service last week
- I have reset the ECU (unplugged for a few hours)

I plan to take it to a LR specialist next week, just a last ditch attempt to see if anyone has experienced anything similar?


* since Feb last year it’s had
- new turbo
- new cam belt/waterpump/fan belt/haldex service/brakes all round
-haldex service
- new wheel bearing
- clutch master cylinder change (&most of the skin from my hands)
- new battery

Yes, you need to get an "air path calibration" after changing the EGR valve.
After changing the EGR valave myself - it started ok but ran rough and after a mile or so went into limp home mode.

Recalibartion sorted the situation instantly.

A friend of a friend did my recal - £30 Jules

Thanks Jules,

Spent the afternoon checking all gaskets and vacuum hoses thinking I’d mucked up somewhere. Good to know it may be an ECU issue, makes sense - hoping I haven’t ran the EGR too much without calibration and damaged it. Will give a LR specialist a call and get that recal sorted, fingers crossed it’s a cheap one also.

AFAIK the recal sets the signal (Im guessing its a PWM signal) for the limits of EGR valve movement - I dont think you will damage it in the meantime. Jules

Just thought I’d update to close this out. Took it to a garage and they diagnosed a bad part. The EGR was stuck open and not engaging properly, even after the recalibration. Took the EGR valve off and sending it back as a defective unit.

Managed to source a replacement valve (OEM) from a scrapyard who assured me it worked. Stuck it back on today and it runs perfectly, no further issues.

Buy cheap buy twice I guess is the lesson here!

Bad luck there.

I bought an OEM EGR valve from Island 4X4 back in 2023 - cost £128 Jules

It is enough just to programmatically disable EGR and there will be no such problem anymore. I completely removed the EGR physically and increased the power to 235 hp 3 years ago and forgot about the problems. //t.me/LRClan