What’s this hose for

Goudy

If it can't work out the air passing the MAF, it has trouble with working out the air temp.

The glow plug one a bit trickier.
It's been getting a low feed back resistance from the plug circuit.
It's been holding open the relay to power to the plugs. this usually means one or more plugs is shot.

As it's historical, it's probably been missing another value to work out how long to keep the plugs turned on, like the air value.
But a modern common rail can utilise the plugs while the engine is running and not just for cold starting, they will turn on and off depending on running conditions to help ignite the fuel, particularly if it's running lean and difficult to ignite.

If these codes are cleared and not returning, then I expect they are a result of unplugging the MAF.
If they haven't actually turned the engine trouble light on, then is looks like they aren't being repeatedly detected (see pend below).


It's important to understand the data and how things work with diagnostic trouble codes and sensors.

Some are easy to understand.
A DTC for a sensor circuit problem is pretty much a yes it's working, no it's not working scenario. 
For example a temp sensor with a short (or it's wiring) will throw a circuit related DTC.
Most sensors work by sending out a 5v signal, the sensor alters that 5v and returns an altered value back to the ECU.
Even with the engine off/ignition on they will return a small value back to the ECU to show the circuit is complete.
If it's shorted/grounded, the return signal is in effect missing.

This sensor could also detect a fault with what it's measuring, say too high or low a signal.
This relies on the ECU being programmed to realise what is too high/low, anything between is variable.

The trouble will a lot of fuel related sensors are that the signals are very variable.
They read and report everything from, ignition on/engine off (the small returned complete circuit value), to start up, to wide open throttle and everything in between.

This means it's difficult to detect and report a value based issue.

What all these sensors and the ECU tends to do is compare what's going on and "pend" a problem.
If the same issue crops up in the same drive cycle something like three or more times, it'll likely set a DTC.
Turn the engine/ignition off after say two detections and it'll start all over again.

So now IF you have a rail pressure issue, the ECU with the ignition on will expect to see no rail pressure and all the way up to something like 2000 bar when running and that individual sensor has problems working out if there is an issue with something in between.

Trying to detect a problem requires it to monitor the signal for a time in the same drive cycle while comparing it to a lot of other sensor data, that might also operate on variable signals.

As the SCV is known issue on these, I would still be tempted to try and turn it 180 degree and see if that has any effect on the hunting idle.
They aren't known to cause DTC's unless the rail pressure drops far too low to sustain running (when the engine starts to cut out).

There are of course other problems that can cause the same problem, like it drawing air into the fuel system.
This usually becomes an issue when the fuel filter has been changed (badly) or there's a crack in the fuel pipes or filter housing.
I'm not sure it's common practise any more, but some manufacturers used to fit clear pipe to the last foot or so before the HP pump, this allowed you to see what was passing through it.

magpies79

As always appreciate the detailed response yeah feel it’s a tricky one as mentioned no engine or warning lights on and I do feel that code with regards to the MAF sensor was a historical one when I started it without it connected.

think I’m going to do as you suggested remove the SCV turn it 180 and see how it runs if it’s clearly better then I’ll replace after the mot in jan.

with regards to the glow plugs how can I find out which ones I have as I do believe some have pressure sensor one kinda hit and miss on which ones had them did read more push to start Astras had them, as the price difference is crazy on normal glow plugs and sensor ones.

Goudy

I wouldn't jump the gun with the glow plugs.

Try and test one things at once.

magpies79

So Goudy been well an interesting week wife was driving the car and stone hit the windscreen cracked it at the bottom to find out that we don’t have windscreen cover and would have to claim against insurance which I’m not doing.

 I put the car through like a pre mot to see what the damage would be and the windscreen would be an advisory but to maybe get it looked at at some point.

he said other then that I’d need 2 rear tyres so mot side not back at all.

car wise not so good as on my way the car has now started to go into limp mode but only on idle when I was at the garage he seem to think egr value maybe take it off give it a good clean I’m still not getting any fault code or warning lights either which isn’t helping.

ive tried taking the egr value off today however I’m struggling to get the last 2 bolts off feel like I’m going to thread the top of it any tips on how to get it off thanks.

Goudy

"Seems to think" is just a guess based on diesel engines habit of caking up EGRs.

Generally EGR issues tend to first show up under load transition, ie moving from part to full throttle or vice versa and getting a bad stutter and judder at those points.

They can cause a rough idle if they are stuck open but you'll get poor performance and bad mpg throughout it's driving range.
The valve should only open when the engine is lean, like on the over run when it would otherwise just pump air.
By letting exhaust gas back around into the inlet it replaces some of this air with exhaust gas, reducing the temp in the combustion chambers, thus reducing NOx.

The emission regulations changed over the years and from around 2006 (I think) that meant things like EGR operation had to be linked to the cars ECU, so when it detects a fault it puts a warning light on.

They do get caked up with an oily, sooty mess (soot from the exhaust gas and oily vapour from the engine crank breather system).
If they aren't too bad it may clean, but if it's had trouble for a while the motor that drives the valve gives up and it can't overcome the crud in there and it's a new valve, so getting it off might not give you the answer.

You would probably be best searching the VX forums or Youtube for removal.
The location and valve changed a bit between engine and model but I believe the Astra J 1.7 cdti one should be quite easy to remove if you remove the valve and it's motor in one. (you don't need to split the motor from the valve to get it off).

It's often the exhaust flange bolts that seize due to all the heat from the exhaust gases and a little localised heat will usually have them moving.
Just be careful if the steel bolts are screwed into an alloy body/thread, the two metals often cause a type of corrosion and the alloy thread is weaker than the steel bolt thread.

Is this your engine/valve?
Opel Astra J - 1.7CDTi - EGR Valve Cleaning

magpies79

Yeah that’s the one and the video I looked at
all straight forward euro car parts have got a sale on and can pick a egr value up for £85 normally £150 I just can’t seem to get the last 2 bolts off on the top 

Goudy

magpies79 said:

 can’t seem to get the last 2 bolts off on the top 

Two of the four on the top holding it down?

You could try driving around until the car/engine is hot and try again.
Or
Put some heat on the bolt heads with a blow torch, but put the other bolts back in and torque them down to try and take from pressure off the stuck ones before trying to undo them.

I would imagine there's a bit of bi-metal corrosion going on between the bolt and what it screws into and you could possible strip the threads in the housing underneath.

If that happens you can get a thread repair kit (commonly called a Helicoil).
You'd need to measure the bolts (M8 or M10's?) and the thread pitch (M8's are usually 1.25mm pitch and M10's 1.5mm pitch) to get the right size coil kit.

They are easy to use if access is good, which is looks like it is.