Have a family members 2002 Octavia here with a problem that is eluding us. Initially it was reported to be going into restricted power mode when overtaking on dual carriageways. Connected it up to my ancient Vagcom laptop and it was showing the boost pressure positive deviation error. Car starts OK but seems to be hunting/misfiring till it gets warm, it will go OK when you drive away but as soon as you push it on a bit in 3rd gear it will get to around 3200rpm and then its like someone has chucked a boat anchor out of the back! Engine still runs but seems very flat and unwilling to rev and the problem does not put any dash lights on. Stopping and restarting the engine cures it till you boot it again.

 

Its a 90 Bhp engine with the standard fixed vane turbo, its done 110000 miles now. This was my car until 90000 miles and was always driven hard and serviced with good quality oil when I owned it but never went near a dealers workshop (other than Jabbasport to have the cambelt done). Present owner drives it in a rather more sedate manor and mainly round town.

 

So far we have replaced the MAF sensor, N75 valve and all the vacuum pipework. Vacuum system is not leaking and turbo pressure pipes are not leaking. EGR valve was choked with sludge and has been cleaned out, turbo pipes are clear and map sensor is clean. Turbo waste gate is holding vacuum pressure so safe to assume diaphragm is not split and it seems to move ok.

 

Will pootle around at "town speed" all week but as soon as you drive it properly this "turbo boost valve positive deviation error" keeps coming back.

 

Open to suggestions as to what to try next??

get a diagnostics done on it see what fault codes pop up its a lot easier then guessing

What year is it?  Are you sure it has a waste gate turbo and not a VNT?

Sounds like typical sticky vanes, but OP seems to be sure it doesn't have that type of turbo, so it must be a early 90 (pre-facelift).  Plus he says the actuator on the turbo moves ok.

 

I would consider checking the CTS and MAP next.

Its not got a VNT (only a 90), Vag com only shows the one fault, "Turbo boost valve positive deviation". which will stay away all week if you drive it like grandpa. As soon as you drive it with any kind of enthusiasm the error comes back when it hits 3200rpm. 

 

Is there a way of testing the MAP sensor? I have access to a decent meter and an oscilloscope etc.

My 2003 90 had a vnt... mbames hit the nail on the head... 99.9%

Yes, earlier 90bhp cars have VNT turbos so I wouldn't be surprised if yours has too.

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This is the actual fault code as it comes up on Vag com.

 

17965 - Charge Pressure Control: Positive Deviation
P1557 - 35-10 - - - Intermittent

 

Common problem on a lot of VAG cars going by whats on the forums but no real answer.

 

The engine is a 1.9 (ALH) in a mid 2002 car. I was convinced it was a standard wastegated turbo but now I'm not so sure. Is it possible to tell from the chassis number or the info tag stuck to the boot floor?

 

When I owned the car (3 years ago) there used to be a squeak come from the turbo area when you lifted of the gas to change gear when the engine was cold. It doesn't do it now...

 

Actuator is moving under vacuum suction though.

Edited 31 December, 201312 yr by trickyhicky

I would say sticky VNT mechanism, but if as you say the actuator is moving freely all the time, it kind of discounts it.  I suggest that you go for a drive logging requested and actual boost pressures and engine speed and see at which point it's over boosting.

 

I've encountered this once before on a pre facelift where the VNT had been cleaned and the MAF and N75 replaced and it was still over boosting.  We did cure it by as a last resort adjusting the operating rod for the VNT mechanism. We verified the adjustment by taking logs of the pressures during subsequent test drives.

Do you get full travel on the actuator (about 1cm, iirc), maybe it part-sticky....

 

The engine code should reveal what turbo is fitted.  It is 3 letters long and on the service book as well as the sticky label on the boot floor  (probably AGR or ALH)

Do you get full travel on the actuator (about 1cm, iirc), maybe it part-sticky....

 

The engine code should reveal what turbo is fitted.  It is 3 letters long and on the service book as well as the sticky label on the boot floor  (probably AGR or ALH)

Difficult to say if it is getting full travel or not as its in such an awkward place and I can't really see whats happening. Can just about get my hand in enough to feel it moving.

 

Engine code is ALH.

Assumed it was a non VNT turbo as the car salesman that sold us the car brand new said so...110 did 90 did not.

 

Never trust anything spouted by a car salesman...

Assumed it was a non VNT turbo as the car salesman that sold us the car brand new said so...110 did 90 did not.

Never trust anything spouted by a car salesman...

Ha ha ha ha ha ha ha...

I had two salesman claim my car was a 1.9 even though it was obviously a 2L before I bought it.

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Had the inlet manifold off this morning and cleaned out quite a bit of caked on black gunge. While it was off gave the turbo a dose of "Mr Muscle" (turns out it is a VNT..). Car now runs and pulls a hell of a lot better and will rev to 4100rpm (was only reaching 3200rpm previously) before it overboosts and throws an error up (same error as before). Also still has the weird "hunting" up and down when it is cold, this goes off if you depress the accelerator pedal slightly to raise the revs to 1100-1200 rpm and disappears altogether after about 5 minutes idling.No fault code showing for this though.

As mentioned before I would look at the CTS. There could be a build up of rust in the turbo as well as carbon.

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As mentioned before I would look at the CTS. There could be a build up of rust in the turbo as well as carbon.

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Can it be tested with a meter, or is it a case of "swap it and see"? Temp gauge seems to read Ok. Had one fail on an old 1.9 Felicia years ago but the gauge showed a low reading on that, seem to recall it affected the way it ran though.

 

Turbo problem had been happening for a year so could well be some corrosion in there if it has been sticking that length of time. Thought we would try the easier option before we pull it apart though.

Edited 2 January, 201412 yr by trickyhicky

Can it be tested with a meter, or is it a case of "swap it and see"? Temp gauge seems to read Ok. Had one fail on an old 1.9 Felicia years ago but the gauge showed a low reading on that, seem to recall it affected the way it ran though.

On the Octavia the CTS is dual circuit, one feeds the ECU and one the dash. With VCDS you should be able to see each signal and see if there is a difference. Likewise with a meter you should be able to see a difference.

What colour is current CTS? Original ones prone to failure are grey whilst the newer improved ones are green.

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