Rough idle on cold start, unless really cold

[RJBingham]

Hi all, my 1.6 hdi has a very lumpy idle when starting first thing, soon settles down once warmed up, but if it's cold, and the glow plugs come on, she runs as smooth as silk for the first few minutes, then back to the rough idle until warmed up, probably something obvious, but not to me 

[notsofast]

Hi all, my 1.6 hdi has a very lumpy idle when starting first thing, soon settles down once warmed up, but if it's cold, and the glow plugs come on, she runs as smooth as silk for the first few minutes, then back to the rough idle until warmed up, probably something obvious, but not to me 

My 1.9 diesel M49 used to do something similar 3-4 years ago.  I think the 1.9 always uses glow plugs except when it's hot, so the lumpy idle usually started after a minute or two.  I never figured out what was going on, though I haven't noticed it the last couple of years, and the only thing I can think that might have improved it is I started using super diesel instead of regular.  After a tank or two of super diesel and at least one good long run, I was sat in traffic one day with a moderately cold engine (i.e. the 'lumpiness zone'), when loads of white exhaust smoke came billowing out - so much that I assumed the head gasket had really blown and I pulled over, somewhat embarrassed. But then before I switched off, after 30 seconds or so, the smoke suddenly cleared and it all was fine, and it now runs cleaner than before and I don't notice the lumpiness.  Maybe the injectors were mucky?

[saskak]

My 1.6HDi (M59; 2007) has been doing exactly this for the past probably 8 years or so. Still to have it sorted and I looked into it properly, so nothing obvious to be honest.

Does yours when doing that have a bit of blue smoke coming out of the exhaust, I bet it does.
My final theory, yet to be put in practice and tested, is that inevitably with age you get a bit more blow-by and on cold tolerances are larger etc., so a bit more blow-by. The original PCV spring is designed to be for brand new engine, tension and height. So, when cold, the spring restricts a bit more than required, oil goes to the turbo as normal, but there is a little bit more excessive crankcase pressure and cannot go back that easy, the PCV restricts a bit and puts the crankcase under a little bit more pressure and the turbo oil return is just gravity and there is push back. So, a little bit of oil gets past the turbo seals and even though the HDi will burn oil, it is not as smooth as diesel+air. Once it gets warm, tolerances are tighter and less blow-by, so then oil from turbo gets back normally into the sump.

It is a theory only, but I intend to test it with extending the spring a little bit and see if the rough idle stops. I do not think you can do much about it, unless my theory turns correct. It could be a slightly duff injector, so you could potentially put an injector cleaner in the diesel tank, but it has not helped me at all and who know if these work.

[dave-murrell@hotmail.co.uk]

Thought I would join in the fun with my ''lumpy engine''.
Mine has also recently started to what I would describe as a misfire until the engine gets hot, waiting for a smoke air leaker to arrive so that I can check for air leaks throughout the system as I have already run a full diagnostic scan (Launch) and found nothing so will will post if I find any firm answers.

[RJBingham]

What bamboozles me, is that it runs as smooth as silk for a couple of minutes when the glow plugs are activated.

[jj9]

On the 1.6 HDi the glow plugs should stay on for approximately 3 minutes (Post Heat) after starting from cold, this happens on every start up unless the coolant temperature is above 70°C.

The glow plugs do not come before starting (Pre Heat) unless the ambient temperature is below 7°C


Are your glow plugs staying on for 3 minutes after starting from cold?

Have you checked that all of the glow plugs are working?

.

[RJBingham]

On the 1.6 HDi the glow plugs should stay on for approximately 3 minutes (Post Heat) after starting from cold, this happens on every start up unless the coolant temperature is above 70°C.

The glow plugs do not come before starting (Pre Heat) unless the ambient temperature is below 7°C


Are your glow plugs staying on for 3 minutes after starting from cold?

Have you checked that all of the glow plugs are working?

.

Only three of the glow plugs are working, but it runs fine if the glow plugs pre heat, for a minute or two, then idles rough for a bit, until it warns up, on a milder morning it idles rough from startup, until warm, when I get a chance, i'll have a look if the glow plugs are coming on post heat.

[jj9]

Only three of the glow plugs are working, but it runs fine if the glow plugs pre heat, for a minute or two. . . 

You really should have all four glow plugs working before looking for causes of a lumpy idle from cold.

I'm curious,  how do you know the glow plugs are pre heating, are you assuming this based on ambient temperature?

The glow plug lamp on the dash gives no real indication of their operation.


Check the power to the glow plugs using a test lamp not a multimeter, this is because a meter may show a voltage that has no power behind it, you won't have this confusion using a test lamp, it will be on if the plugs are being fed and off if they're not.

Wire a semi permanent test lamp to one of the wires that feed one of the glow plugs and place inside the car, then you can monitor exactly when they are operating.

.

[notsofast]

Only three of the glow plugs are working, but it runs fine if the glow plugs pre heat, for a minute or two. . . 

You really should have all four glow plugs working before looking for causes of a lumpy idle from cold.
.

Yeah, another time when my M49 had lumpy running from cold, the cause was found to be the glow plugs. The symptoms were perhaps slightly worse than yours - I also got white exhaust smoke as well as jerky throttle response, and it happened every morning (in January) - but then the garage found that two glow plugs were defective, so your symptoms could well be the result of just one being faulty.

[saskak]

Well, my "smokey" 1.6HDi (2007) M59, had all 4 glow plug replaced (a while ago) and the relay for a good measure and still smokes/lumpy for the first 20sec or so when cold of course. I do not think most of these "problems" are the glow plugs. The 1.6HDi does not need them that much unless really cold as per jj9's comment and compared to the M49 for example.