Lumpy idle on startup that clears

[JJCaddy2024]

Got a 1.6 TDI, and before I jump the gun on injectors, wanted to see if anyone has any experience with this issue.
On startup when cold only, the van will idle rough for approximately 20-30 seconds before sitting back smoothly at about 900/1000 rpm.
As mentioned it’s only on cold start up, and will run smooth for however long I drive, for example I did a 7 hour trip non stop after startup and it ran like a dream.
From what I’ve seen online there’s a long list of potential faults, EGR valve, DPF, Injector, fuel, air intake etc.
I’ve checked the basics, air filter is brand new and no blockages, fuel seems to be delivering as it should, so can rule out the fuel pump, injector values on OBD seem to be quite similar with no irregularities. I’ve also started using Shell V power as it was suggested to try that, 2 tanks in (and an empty wallet later) and it hasn’t changed much, but does seem to run quieter!
Is there anything else I can check visually or with an OBD tool which might point me more in the right direction or is this a tell-tale sign that the injector(s) are on their way out? I’m aware the main failure is electrical based on injectors, which is why I’m hoping it’s something else, or I’d imagine I’d be getting some fault codes.
If it helps it’s engine code CAYD.
Any help would be greatly appreciated.


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[STP]

I had this on a TDCi and it was the egr valve sticking until the engine warms up a bit.

[JJCaddy2024]

Cheers pal, will have a look into into it, seems the more I look the more it seems to be that!


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[Robbi3]

When starting from cold, do you get a bit of smoke coming from the exhaust?
Mine is a bit lumpy on start then clears once warm, just interested if your problem is the same.

[STP]

My TDCi was like that, it smoked like the red arrows and ran really lumpy for about a minute until the coolant temp got over 50 and then ran sweet all day after that. Hot starts were fine.

It was the egr valve and everything else was spot on. I know it was that as I tried absolutely everything else, then blanked the egr off and it stopped immediately. You can't do that of course or it will throw an engine light (the one I blanked was an 07 so it didn't really care about the egr flow going missing)

My best guess is that it was sticking open after it all cooled down and when commanded to close, it didn't do so until it got hot (sticky sooty crap etc) so on cold start it was wide open and on full recirc when it should have been shut.

[JJCaddy2024]

No smoke Robbi3, just the occasional lumpy idle, it hasn’t done it the past few days, even when left to go stone cold! Starting to think the EGR Valve sticking is probably the main cause at this rate, can’t see it being anything else, tested my glow plugs, checked my injectors and watched some live figures through my OBD reader with no real answers! Considering a potential blank but not sure yet! Might as well get a little remap at the same time and get a little more poke out of it!


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[Robbi3]

JJCaddy2024. If you know someone with VCDS, they should be able to output test your EGR valve or give it a good clean.

When you tested your glow plugs, it is a good to test with a multimeter using current setting not voltage.

They should all roughly draw the same current, because they have a metal internal coil which eventually wears out due to heating/cooling.

[STP]

I'd bet £100 it isn't the glow plugs. I recorded live data for days, changed the glow plugs, and the relay, nothing helped. Smoothing out as soon as the coolant gets above 50, it is not the glow plugs.

Blank the egr to see what happens, even if it throws an engine light it will prove that's the issue. Plates are on eBay for a few quid. Only thing is that it's hard to get to on the TDI.

[JJCaddy2024]

It’s definitely not glow plugs for me they were spot on, 0.8A across the board and nice and clean. As STP says I’m going to probably go with an EGR delete, seems the most logical solution, will see if I can get it done myself, just struggle for space to do it!


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[Robbi3]

@STP if you blank off the EGR does it give a permanent engine warning light?

@JJCaddy2024 please keep us updated on your progress with your EGR delete, looks like I may have to go down that route.

[STP]

I did it on an old TDCi with no issues, but I think on ours then you may get an engine warning light for low egr flow or high airflow (MAF airflow increases if the egr is blanked when it should be open)

[Robbi3]

STP Thanks for the reply, something I may have look into with my lumpy coldstart.

Maybe a resistor connected to the EGR plug across the 2 sensing cables, could trick the ECU to not give a CEL.

[STP]

The error comes from the MAF airflow readings which should drop when the egr opens, as some of the intake is being recycled, instead of pulled from outside.

The ECU knows this and flags a fault. I doubt you could influence that by making it look as if the egr is still there, plus it's a servo unit which can be commanded to any position between 0 and 100% so the ECU would quickly realise it wasn't working.

[Robbi3]

STP Thanks for the info about the MAF and the EGR, very interesting .

[STP]

The best thing you could do, is get it mapped out of you could be sure it was actually closed (perhaps commanding it to close by using a diagnostic tool and then mapping it out) as the soot it puts back into the intake is evil.

The egr was introduced early on in NOx control as they realised less oxygen means less NOx and of course increasing clean air regulations required control of oxides of Nitrogen. Air (well oxygen) when partially burned generates NOx and this was an attempt to lower it. Adblue is the latest version of that.

The egr is the work of Satan.