Hi, Erratic idle is usually caused by air leaks & the PCV hoses beneath the inlet manifold are the usual culprits especially as you have replaced part of it.
Exhaust gas temp fault will mean it will running with a rich mixture.
It does appear you still have a leak on the boost pipework.
N75 can test as in spec but can still be faulty.
Hoggy.

 

You definitely want to sort out the EGT sensor, new ones are expensive, people have managed to fix them, if a fault in the electronics end.

That won't be causing the low boost... but you probably want to measure what the boost pressure actually is? You cash test the actuator with a hand pump and gauge.

 

Thank you @Hoggy and @StuartDB, appreciate the pointers. Sounds like removing the intake manifold and going through the PCV pipework is sensible. There is so much piping and valving on this engine, it is a minefield for potential leaks.

Very interesting to know that the EGT will be forcing a rich fuel mixture too, as the car does struggle to get through MOT emissions. The data PID for EGT is returning a constant 110 deg C on my diagnostics reader, so feels like an electronic/wiring fault rather than the sensor itself - I shall do some more searching to see if there is a way to test it.

Martin.

 

No need to remove the inlet manifold just the trim around the dip stick tube and the dip stick itself, although have a spare as there known to break when you remove them. The pcv system is prone to splitting given the age of these cars now. Awesome gti sell a 034 motorsport kit that includes upgraded pcv 034Motorsport Breather Hose Kit - 1.8T 225bhp (AMU) Do you have anyone local with a working 225 to swap the N75 and rule that out?

 

What reader have you got the PID configured for the VAG EGT?

As Android Torque Pro cannot see the EGT sensor. Also some of the sensors have multipliers set up?

A faultly EGT usually sends back something like 1199°C or similar (whatever the maximum is) or null (open circuit)
Try unplugging the EGT (infront of the inlet manifold) and see what reading you get then?

If you have the PID details, I might try and add them into Android Torque Pro?

Prolonged use running with a default fueling, will probably eventually break the pre cat o2 sensor.

 

What reader have you got the PID configured for the VAG EGT?

I use something called iCarsoft CR Pro. Initially bought it on the recommendation of fellow E-Class owners, but it seems to do a great job on the Ford, Audi, and Mitsubishi cars I have tried it on since.

A faultly EGT usually sends back something like 1199°C or similar (whatever the maximum is) or null (open circuit)
Try unplugging the EGT (infront of the inlet manifold) and see what reading you get then?

In a quirky twist of fate, it was actually unplugged. Mine returned 110 deg C exactly, and consistently whilst unplugged.

If you have the PID details, I might try and add them into Android Torque Pro?

Does this help? I have tracked the live data, and it reads sensible, changing values so tend to believe it is correct.

Prolonged use running with a default fueling, will probably eventually break the pre cat o2 sensor.

Good point, and alas that may well be the case for me. The car has been running for a couple of years at least with the EGT disconnected.

Martin.

 

Thanks again for all the pointers all, this has really helped me today. Found out that the EGT was not actually plugged into it's control box, must have disconnected it a couple of years ago when we did the cambelt! I would not have known where to look without the suggestion to take the inlet manifold vanity cover and dipstick tube bracket off. Have only had chance to drive 10 miles or so since re-plugging in the EGT - this fixed the EGT fault code of course, but naturally not the pressure drop fault code.

Found another couple of possible leaks too, but only leaks at 15+ psi. I am not sure if these two pieces are designed as some sort of pressure relief valving - any ideas? My understanding is that the car should produce about 0.9bar (13psi) so perhaps designed to operate this way.

Really appreciate all the pointers and help everyone, such a great help to me.

Martin.

 

Hi, If they are leaking under pressure, more than likely they will be leaking under vacuum & sucking in air upsetting the A/F ratio.
Hoggy.

 

I thought you said it always reads 110c?

Oh hang on you're saying it has simply been disconnected for years?

 

You might find your running improves, you need to clear all the engine faults even if there are none displayed as that will reset your fuel trims.

 

Also that plastic puck shouldn't leak, it is not designed to act like a relief valve, it is leaking down the seam.

 

My quest to solve the low boost issue, and the boost leaks continues. I have found leaks in some pipes, and in the plastic puck, and have replaced all of those successfully.

Performing another 15psi pressure test between airbox outlet and inlet manifold inlet (as per first post), I have a leak from what appears to be a deliberately drilled hole in the airbox end of the cylinder head - very confusing. Photos below, but does anyone know whether air should be able to leak from here, or if there should be some sort of bung in there? I have looked at the online parts catalogues which mention no bung (nor the hole itself), and a google image search is not throwing anything conclusive my way.

Thanks,

Martin.

 

Are you sure it is drilled hole not the EGR? Also connecting to sai if you have one, which also connects to airbox.

Realize it's bam engine comes with no EGR if I remember correctly


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That looks like half moon seal area under the chain tensioner. There is a thin gasket and half moon rubber bung under the tensioner and are known to leak.

 

Thank you @fire88 and @davebowk. I really appreciate the help, chasing boost leaks seems to be a full time job on this engine [emoji23].

It may well be a half moon rather than a full circle. Access is very tight so it is difficult to feel that area, I did not want to remove the camshaft adjuster to check in case it needs a new gasket - thus disabling the car completely.

There is definitely a completely open half moon/hole though, not just a leak. I can push my finger right through. I shall have to break out the trusty Haynes manual and investigate more - I assume the cylinder head (aka rocker) cover has to come off to get at this gasket and half moon seal?

Martin.


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Yeah... cam cover off... but why is there no oil leaking out of it?

 

Thank you everyone for the continued help and pointers. Unfortunately, I only get the odd hour to work on it so the replies and updates are sporadic - your tips are helping me as I know more about where to look.

So, I have dismantled a bit to get better visibility of the cam cover gasket. The half moon seal is in place, it is just further back toward the firewall. To nobody's surprise, it does appear to be leaking oil as there is some significant oil deposits there. The half moon 'hole' immediately behind the cam adjuster, where I have my air leak, is spotlessly clean - no oil leaking there at all. The cam cover gasket in that area of the engine is 20mm further inboard, so I am pretty confident there is not meant to be any sort of oil seal there.

The 7zap parts catalogue suggests there is some sort of cap/cover that goes over the air leak hole that I have. The shape is wrong in the online picture, but that is not unusual in my experience for parts diagrams.

I think the cam cover needs to come off alas, both to fix the leaking half moon seal, and to investigate how air is getting to this hole.

Martin.

 

OK, I think this is making some more sense now - more perusing of that parts diagram has helped.

Looks like part no. 14 is the gasket that is relevant to my air leak 'hole', and when I search for photos of that actual part, it seems to come with a half moon bung too. Looks like that half moon is missing on my car for some reason.

Thanks for everyone's help, looks like this is the missing piece of the jigsaw.

Martin.

 

Underneath that gasket number 14 there is also a rubber half moon bung. You need a chain tensioner tool to change them two.

 

"Thanks for everyone's help, looks like this is the missing piece of the jigsaw."

that's optimistic, it is maybe just another thing....


have you actually logged your car? not scanned for faults - but actually logged what the car is trying to do and what it is actually doing?

 

that's optimistic, it is maybe just another thing....

I know you are right, but let a man have a small victory won't you .....

have you actually logged your car? not scanned for faults - but actually logged what the car is trying to do and what it is actually doing?

'No' is the short answer. My diag kit has the ability to log data - do you have any recommendations for PIDs to try and log? The main challenge I see - perhaps only in my specific case - is that I cannot get any PIDs to show boost pressure - there are literally tens of pressure related PIDs that my diag kit presents me with, but they all seem to show N/A as values when I view them on live data. I don't particularly want a boost gauge in the car, but can install one in the glovebox if necessary.

Martin.

 

it's usually just "vacuum pressure" they are HG when in vacuum and PSI under boost.

I posted on that other thread with boost issues the common items to log when evaluating issues with these cars