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Discussion Starter #1
Hi all. First post here. Looking for some advice on where to go next.

My Astra J with its second 1.7cdti engine (the first one blew up) has a bad hunting at idle.

This was also happening on the previous engine. DPF has been removed but not reprogrammed out of the ECU yet.

I have changed the Denso fuel valve, cleaned out the EGR valve which is opening and shutting correctly, changed the crankshaft sensor.

There are no fault codes coming up

Where next? I have just watched a Astra H video with similar symptoms and that was the throttle body being gunked up.

tempted to go there next
 

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Where did you get the replacement SCV from. Try blanking the egr but i suspect the SCV is faulty.
 

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Discussion Starter #3
It was an eBay job.
However, the car is exactly the same as with the one I took out. No change at all.

When it first starts for about five minutes there is thick white smoke until the engine gets some heat in it.

My knowledge is pretty limited but my guess would be the air mixture with the fuel is off. Which is why I cleaned out the EGR then was tempted to do the same with the throttle body.

is there any sensor data which could point me to where the fault is likely to be. Can I rule out the scv valve by looking at the sensor data rather than buying a new one only to find nothing changes?
Thank you
 

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Discussion Starter #5
Unfortunately that bit I don’t know.

I recall him saying that the new engine came out of a 64plate which is the newer model to mine and he said he had to put all my old engine bits back on. So I’m assuming just the engine block itself is new and the rest is mine like all the valves, filters etc
 

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Discussion Starter #6
For example I just took it a mile down the road to Tesco. The white thick smoke stopped half way and when I got there the idle rpm had gone up to about 1200 from 850 albeit hunting very badly
 

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Then i suspect its trying to regen the dpf, you need to get the software done before proceeding or you may be trying to correct something thats being activated by the ecu.
 

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Discussion Starter #8
That did cross my mind. But was curious to how or why it would hunt so badly.

My original engine did it but not as bad. I did for two years on a regular basis get the dpf warning to continue driving and I would take for a blast and rev the guts out of it to blast it out.

I’m currently getting around 60mpg which I much better than my previous engine so not all complaints
 

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The injector post injection duration is increased during regen which will cause a rough idle, most cars will enter regen and carry on regenerating at idle, the give away is the increased rpm and rough idle, if you dont get the software done you run the risk of increased oil level due to post injection diesel being forced past the rings into the sump, this will dilute the oil and if not corrected will result in an engine runaway, if it was mine i would have a dpf/egr delete done and go from there.
 

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Discussion Starter #10
It’s booked into have that done next Friday. £150 seems reasonable.

I will report back following that to see if any idle/rev progress was made.

Thanks for your help, so far 😉
 

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The injector post injection duration is increased during regen which will cause a rough idle, most cars will enter regen and carry on regenerating at idle, the give away is the increased rpm and rough idle, if you dont get the software done you run the risk of increased oil level due to post injection diesel being forced past the rings into the sump, this will dilute the oil and if not corrected will result in an engine runaway, if it was mine i would have a dpf/egr delete done and go from there.
Hi Andy,

I noticed today during idle when it was at its worst. On the scan tool the EGR error sensor is jumping between 0 and 100%. Almost in time with the hunting. Sounds suspicious?
 

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During regen the egr is used to help increase combustion temps, its also used at idle, with no dpf in place your ECU will give lots of strange readings, i would have your software done and see what happens after.
 
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