Jerky when cold 1.9TiD

[warmrain]

We have recently acquired a 9-5 yr2006 1.9TiD diesel and I have put it through a full main 72k service with all filters changed (oil, fuel filter, air filter) plus cambelt etc.  However it does not drive smoothly at low speeds when cold. If I try to trickle it slowly along the driveway in first gear between 1000 to 2000 rpm before the temp gauge has reached normal, it is very jerky and pulses back and forth.  My 2.3 petrol aero drives perfectly smoothly under the same conditions when cold. 

I am new to diesels and wondered if this is normal for this diesel or what other individuals' experiences were?

I also had a new EGR valve installed at the service but it hasn't made much difference to the jerky cold running at low revs.  Any thoughts?

[Max Headroom]

Hi Warmrain - I'm pretty new to oil-burners as well. One of the first things I discovered is that they are definitely not so "tractable" at low rpm - try give it slightly more welly than you would with a petrol machine and I think you will find there is no problem.
Pulling out onto the road from my drive is uphill, and when cold mine seems to struggle a bit compared to the wife's 1.8 petrol Meriva so there is bound to be a big difference with your other car!.
My dads diesel BMW is even worse than the SAAB and I really have to give that a good boot

See how you get on and report back, but I don't think you have a problem

[Audax]

I'd get it on tech-2 and check for any software updates, you'll need a good specialist or dealer for this, call them up and ask if they can carry out any necessary service programming for your car. Also when they do this make sure they read the fault codes stored in the ECU the fault codes for some faults will not necessarily put the check engine light on so you may have a faulty glow plug or some other problem developing.

[warmrain]

I have tried my code reader on it and there are no engine fault codes stored.  Re glow plugs -- I would expect them to be switched off within a few seconds of the engine firing --or is that not correct?

What should the engine coolant temperature read (in degrees Centigrade) when "warmed up" -- ie. after running the car for half an hour or so? 

And is the temp sensor reading (ie. probe) on the "inside" side of the thermostat valve and reading the temp of the water jacket around the engine block, or on the "outside"?  ( I am trying to determine whether the thermostat is opening too early; or in fact stuck partly open).  A new thermostat for a 1.9tid diesel is not cheap!

Thanks for any help.

[Max Headroom]

You don't say who serviced it - was it a SAAB workshop?

[warmrain]

Serviced at my local Saab specialist chap. (He used to work for for the main dealers until he went independent).

[sgould]

All Saabs have electronic temperature gauges.  They are controlled to sit at "9 o'clock" (once warmed up) if the temperature is within acceptable limits.  It will only move from there if the engine is too hot or too cold.

[warmrain]

Ah.  I am not referring to the temp gauge on the dashboard but the live readout of the coolant temp via my code reader.  If the sensor is on the "outside" of the thermostat, then my reasoning is that the temperature reading should stay pretty low until the thermostat starts to open.  Anyone with a detached thermostat to see where the sensor is? -- as I believe it is integrated with the thermostat housing.

With the engine driven around for half an hour, the reading is 75 degrees Centigrade.  Seems a bit low do you think?

[Audax]

I have tried my code reader on it and there are no engine fault codes stored.  Re glow plugs -- I would expect them to be switched off within a few seconds of the engine firing --or is that not correct?

Not  correct on a 1.9 diesel, they are used for the particulate filter regeneration and are most certainly not used just for a cold start!

[warmrain]

From cold it takes about 5 miles of driving to get the dashboard temp gauge to come up to "normal"--- ie. indicator needle almost level at 9 o'clock.  Is this normal for this diesel as my petrol aero doesn't take half as long? 

[Max Headroom]

I think I've had this discussion elsewhere in the forum, but just as a comparison, in cold weather that we had in Dec/Jan My car is fully warm (needle at 9 o'clock) after approximately 3 miles of undulating country roads (no steep hills) at normal speeds and acceleration

[warmrain]

Thanks for that useful comparison.

I am beginning to feel that my thermostat isn't quite right because, although the coolant temperatures get up there eventually, it does seem to do so slowly and it must be a little "sticky".  Or it is already partly open when cold and I am getting unwanted radiator cooling from the start.

[warmrain]

An update. 
I have finally taken the plunge and changed the thermostat. Not an entirely straightforward decision as it didn't seem entirely "broken".  The dashboard gauge would show a needle hovering almost at "9 o'clock" or just a few degrees below and it would move about between that small range.  The car seemed to drive alright after the first 5 - 6 miles.  As the thermostat on a 1.9tid costs six times as much to change as on the petrol engines, one needs a good reason to "try a new one".

However since putting in a new thermostat, the temp gauge stays absolutely stuck at 9 o'clock -- however I drive, slow fast, or whatever the traffic conditions --- and my mpg improved  immediately by 2 - 3 mpg!  The moral of the story is that if the temp gauge does anything other than stay absolutely GLUED to 9 o'clock, your thermostat is faulty (unless your fan has stopped working or you have lost all your water!).

Still, even with the improvement in mpg, I reckon it will take me about 16 full tanks of diesel or about 10,000 miles before I recoup the money spent on the new thermostat (parts+labour).  .. and Oh, the car warms up in 4 miles rather than six now.

[Audax]

It doesn't help that on the 1.9 that the thermostat is an entire housing that is fairly inaccessible so it's not a cheap part or a cheap job especially when compared to the petrol cars.