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[pscocoa]

Hi all - not had too many car issues in recent years but just hoping to get a bit of a strange one sorted today.

The Insignia 2.0 diesel auto (2012 93000 miles) has variable revs when at idle which has gone a little worse over last 3 weeks so that you now get a slight hesitation - again only noticeable at idle. The DPF warning came up just before this (say 4 weeks ago) so we gave it a run but haven't done any longish runs since. Took it to independent yesterday who read codes and showing DPF 86% blocked and cylinder low pressure. As they could not do forced regeneration they asked my permission to do cylinder leak test to which I agreed and later in day they came back with no issues and that the fault appears to be one glo-plug (type which has pressure sensor). I had googled all of this and Insignia sites have a lot of posts where this idling issue is prevalent - some have changed loads of parts, others ignore it.

Hoping today brings result but not sure why diagnostic wouldn't go straight to glo-plug fault?

[STEMO]

The 'Service vehicle soon' message shows if it's a glow plug, Phil. The codes have to be read, of course, to show which one(s) it is. But my Astra used to drive as normal even when a couple of glow plugs were needed, no uneven idle. There are plenty of places who will bring your dpf back from the dead, here's one close to me:

https://www.yorkshiredpfcentre.com/dpf-cleaning

[JasonH]

Once the car is fully up to temperature the glow plugs should be fully out of the equation. So a bad one shouldn't affect the idle when the engine is hot.

If you have a blocked DPF it could be soot or ash. If it's soot then a regen will sort it. A few hours on the motorway is an effective regen, even if the car isn't actively trying to perform a regen.

If the DPF is full of ash (the residue from many soot regens) then the only solution is to replace it or wash it out. Washing them out is messy but 100% effective, I've done a few now. The DPF's are ceramic and to get the ash out you can only force it out at the engine end, i.e. pressure wash from the exhaust end. That's obviously with the DPF removed from the car!!!

I'd get your DPF sorted then see how the car runs.

[Andy B]

Once the car is fully up to temperature the glow plugs should be fully out of the equation. So a bad one shouldn't affect the idle when the engine is hot. .....

Not so with a pressure sensor glow plug  I'm sure that Mark will be able to give us an idiot's guide to them. 

https://www.borgwarner.com/aftermarket/diesel-cold-start-ignition/pressure-sensor-glow-plugs

and they're a f*** site more expensive than a glow plug of old.

[STEMO]

Once the car is fully up to temperature the glow plugs should be fully out of the equation. So a bad one shouldn't affect the idle when the engine is hot. .....

Not so with a pressure sensor glow plug  I'm sure that Mark will be able to give us an idiot's guide to them. 

https://www.borgwarner.com/aftermarket/diesel-cold-start-ignition/pressure-sensor-glow-plugs

and they're a f*** site more expensive than a glow plug of old.

£120 a pop IIRC.
They heat the cylinder up, when necessary, to ensure maximum efficiency and less emissions. Load of old cobblers. Still can't see how they would affect the idle speed.

[pscocoa]

Thanks guys - glo plug pressure sensor was the problem.
Basically the glo plug part was working but the pressure sensor part of it was faulty- hence it did not throw a glo plug code but because there was a fault in the system the regen would not work. All seems good and forced regen worked.

[Marks DTM Calib]

The 2.0 CDTi glow plugs also monitor the cylinder pressures, I suspect a faulty one would show a low compression fault code and might also cause a change in the idle. It sounds like this is a confirmed issue given the codes and the fact the cylinder pressure is measured as good so the first job should be to repair this.

DPF regen gets inhibited when many engine faults are active, this is done to protect the system/engine from overheating or bore wash during the active regen phase.

So change the glow plug, ensure the codes are cleared, check the live data to confirm cylinder pressures are good, and go for a good drive to regen the DPF (forces regen should be avoided if possible!), if it does not regen then do a forced one.

Not rocket surgery but, we all know how to many mechanics struggle with the basics these days

[STEMO]

The 2.0 CDTi glow plugs also monitor the cylinder pressures, I suspect a faulty one would show a low compression fault code and might also cause a change in the idle. It sounds like this is a confirmed issue given the codes and the fact the cylinder pressure is measured as good so the first job should be to repair this.

DPF regen gets inhibited when many engine faults are active, this is done to protect the system/engine from overheating or bore wash during the active regen phase.

So change the glow plug, ensure the codes are cleared, check the live data to confirm cylinder pressures are good, and go for a good drive to regen the DPF (forces regen should be avoided if possible!), if it does not regen then do a forced one.

Not rocket surgery but, we all know how to many mechanics struggle with the basics these days

Nor brain science 

[pscocoa]

The 2.0 CDTi glow plugs also monitor the cylinder pressures, I suspect a faulty one would show a low compression fault code and might also cause a change in the idle. It sounds like this is a confirmed issue given the codes and the fact the cylinder pressure is measured as good so the first job should be to repair this.

DPF regen gets inhibited when many engine faults are active, this is done to protect the system/engine from overheating or bore wash during the active regen phase.

So change the glow plug, ensure the codes are cleared, check the live data to confirm cylinder pressures are good, and go for a good drive to regen the DPF (forces regen should be avoided if possible!), if it does not regen then do a forced one.

Not rocket surgery but, we all know how to many mechanics struggle with the basics these days

Thank you - glo plug changed and all good so far. Just a bit of a long way round to get there. I suppose with hindsight and knowing that only part of the glo plug will throw a code pointing to the glo plug then it would have been  an idea to swap a glo plug over from a cylinder which was not exhibiting a pressure issue. Anyhow - job done now.