(Henceforth shall ensue a slightly wordy explanation of what's what, followed by a probably simple question.)

I've had my (3-year-old main-dealer-approved used) Octavia 3 weeks now and already love it to pieces. A few little niggles with it that have been mostly ironed out by my local dealer under the warranty.

They've nicely sorted the drivers door tweeter speaker for me and also replaced the coil packs without me even asking them to as they noticed they were the type that go wrong. Very pleased with that.

But (there's always a but) a friend of mine bought himself VAGCOM a while ago to use on his Seat Leon and we decided to plug it in to see what was what with my car, fully expecting no problems as I'd expect things like that to be covered by the 6-billion-point used-car check that the dealer is supposd to do.

There was an engine code - 17608 - that I have already extensively researched on the net and in my opinion (and that of my friend) it's "probably" the DV causing it.

I told the dealer, mentioned the DV, he rolled his eyes and made noises like they do DV's all the time.

They looked at it.

They (surprise!) DIDN'T replace the DV. They replaced the solenoid valve that sits next to the DV and said all was sorted.

I was a little bemused as I expected them to have replaced the DV. When I got chance to plug VAGCOM back in I found the engine code still there. We cleared it, blipped the accelerator pedal to rev the engine, rechecked the fault codes and it had reappeared.

So I rang the dealer and said I thought they probably should replace the DV. He said "we did". After explaining that they hadn't as I could clearly see new jubilee clips on the solenoid valve he said "oh" in a way that sounded like there'd been some miscommunication between him and the workshop and asked me to take it back.

So today I did that. And they checked it with the computer (again), cleared the fault, took it for a test drive and the fault came back (well duh!). And once they'd done all that he said to me "well, it seems to run alright" and appeared to be trying to get me to just accept things and go away.

He finally decided that they could let me have a car next week and keep mine for a couple of days to try and find out what is causing the fault code, including "one of us taking it home and trying it in the morning from cold with the computer" (most odd in my opinion - the fault certainly shows up when it's warm so they want to try it from cold? Huh?).

However, I'm thinking that this is getting a little silly now. So here are my options. Opinions welcomed please.

Should I just ignore the warranty and buy myself an OEM DV (I see no point in spending 3x-4x as much for a Forge), fit it myself and hope that clears the problem - obviously taking it back to them if it doesn't sort it?

Should I tell them that I'll gladly PAY for them to replace the DV but if it turns out that it clears the problem then I want it done as a warranty job?

Perhaps should I just ignore the engine fault code? That option does jarr a little as I reckon that I ought to be able to have a ECU-fault-free car if it's warrantied...

Or am I barking up the wrong tree with the DV theory and should just let them do their job, no matter how long it takes or how often I'm without my car?

Qorb

(edit PS when lifting off the throttle there's a fluttering noise a bit like, errm, rippling through the pages of bent paperback book with your thumb - the dealer guy said "they all do that")

If you're local to Aylesbury (or London Docklands) then you're most welcome to my old OEM DV. Free and for nowt.

Get THEM to sort the DV under the one year warranty they should have provided - then replace it with a Bailey/Forge or whatever and keep the new OEM DV as a spare. I think the rippling noise is the wastegate operating. Others will advise if/when that is a problem, but I think what you are hearing is perfectly OK.

A nice offer Quinten but sadly nowhere near. I think, having deliberated a bit, that I might go down the route of offering to pay for the DV fitting if it doesn't cure the problem. That way if my intuition about it is correct then I get the warranty invoked without having to feel like I'm fighting with them to get them to even TRY a new one in there.

Depends how much they quote me for the part plus 10-minutes labour though

Cut-off valve (DV) - AGU, AUM, ARX engines

06A 145 710 N -

Take it back to the dealer and ask them to look at (and I mean, take it off and inspect it) the DV. The "rippling" noise you describe is almost certain to be caused by a split diaphragm. My 1.8T made the same sort of sound before I had the DV changed for an aftermarket one; it turned out that the diaphragm had split. Apparently the OEM DV uses a cheap plastic diaphragm which is prone to splitting.

Once you have got the dealer to sort out a replacement DV, keep it for an emergency. Buy an aftermarket piston type (e.g. Forge, Bailey, etc.) and fit that instead. It probably won't affect your car's performance (although some say it's more responsive), but it will certainly be more reliiable.

I've been quite insistent on the DV front with them already and they are very (VERY) reluctant to go for it on a hunch - probably because they don't have the guarantee of someone footing the bill. If they go to the trouble of taking it off and inspecting it (or even replacing it) and it doesn't clear the fault code then the warranty people aren't going to cough.

If I volunteer my dosh then I can see they'd probably do it for me even if the DV doesn't end up clearing the problem. Wonder what they'll charge for the labour - do I mention that I know how easy the job is or do I let them try to sting me first ... I guess I'll find out tomorrow when I ring em

(edit PS when lifting off the throttle there's a fluttering noise a bit like' date=' errm, rippling through the pages of bent paperback book with your thumb - the dealer guy said "they all do that")[/quote']

Sounds like waste gate flutter and potentially not good for your turbo.....I think boost has no where to go and vents through the waste gate. Would point to a dodgy DV.

May be one of the Wisened Ones will confirm this or otherwise.

Bite the bullet and upgrade to a Piston type DV. Then take the 'old' DV into the dealer and tell them you had to replace it cos it was knackered. Insist that they fill in a job card and make some excuse up why you thought it was knackered - drop in performance or similar. They should then send it off to Skoda UK and you should get a phone call in a week or so from the dealer asking you to come in and pick up your 'new' OE Bosch DV - which you keep as a spare.

It worked for me when my OE N75 valve was fubar (the solenoid valve you mentioned). Just a thought....

See that N75 right ... I was under the impression that was the N249. I have this whole theory in my head of which bit does what and I thought the N75 was the wastegate solenoid (causes exhaust to bypass the hot-end of the turbo thus reducing/ceasing boost as required) and the N249 was the boost-control solenoid (switches the DV to source from the vacuum reservoir momentarily to backvent some boost to control it into the engine?) - the N249 being the one closest to the DV. If that one is really the N75 then my brain is all backwards and I'm getting confused again

I've hunted the net for a decent piccy showing the basic air/exhaust/vacuum interconnects to aid my sanity but come up blank - is there one knocking about on here somewhere?

Will be ringing them tomorrow (didn't get chance today) to suggest the "I'll fund it if it ain't broke" option. Worst case I end up with my 3-year-old DV replaced and hooked up to handy jubilee clips for future replacement (I'm assuming it's never been replaced in 35k miles if it's still got the original crimp-fitments on it...?)

The more people that say "sounds like the DV" the more confident I am that the warranty will end up picking this one up anyway

Is this of any help?

The N75's part description is electro change-over valve, ie:

Electro change-over valve (N75 wastegate regulator valve) - AGU, AUM, ARX, AUQ engines

058 906 283 F -

How bizarre. The fault code on my Octy says specifically N249 on both VAGCOM and the dealers unit hence that's what I'd expect them to have changed (the guy even told me "turbo recirculator valve" on the phone which is what their error code calls it) but they replaced the N75!?!? The mind boggles ...

(/aside - where's the N249 then!?)

p.s. ta v.m. for the piccy

I think there are a number of so-called electro change-over valves associated with the 1.8T's engine, and working out which is which, eg N75, can be a problem. I will try and identify the N249 tomorrow when I can get at ETKA.

Ah here we go. Here's one I found (in French) that kind of explains what the N249 does - and this is why I expected it to be near the DV ...

http://www.leon-concept.com/dossier/20vt/#aire

This also infers that the DV is used for more than a simplistic "dump valve" to stop the turbo stalling when the throttle is backed off and I've not seen anyone mention this particular use of it on the site.

Time to get my personal interpretation of how this is all working sorted out I think ...

This is all "my interpretation" so any corrections or further explanations would be welcome so that I vaguely know what I'm on about when talking with the dealer

From what I've read, the N249 can switch the DV's vacuum port to feed from the inlet manifold (vacuum controlled by how open the throttle is) or directly to a "hard" vacuum provided by the reservoir (formed by inlet vacuum inside that plastic tank via the one-way valve).

The N249 can switch this very rapidly according to somewhere else I read (in the order of tens-of-millisecond opening/closing times) which allows the DV to be held anywhere from fully closed, through various states of partly-open, to fully open by the rapid presence/absence of vacuum, hence allowing the ECU to control, at any given moment, how much of the boost being generated by the turbo actually reaches the engine (the excess being recirculated).

When fully off the throttle the DV is open anyway through normal inlet vacuum and all the turbo pressure (or as much as can fit) is recirculated to stop the turbo stalling (which is presumably perceived by many to be the sole purpose of the DV?)

Dull question time - if the ECU can control the boost so quickly and accurately using this mechanism, what use is the wastegate which, to my simplistic brain, would be a much slower and cruder way of regulating boost presssure? Are there situations where you would want the turbo NOT being spooled by the exhaust gasses, irrespective of controlling/dumping/recirculating any boost that was made?

My brain hurts. Time to stop for a bit

p.s. such fast modulation of the DV would probably explain why they wear out so quick, plus perhaps explain why tougher springs that can/are fitted in forges etc may indeed help with preventing turbo stall on gear changes, but could screw up boost pressure regulation if the N249 control in the ECU can't deal with having to switch to the hard vacuum so much - or perhaps that hard vacuum doesn't last long enough to handle the harder suck needed to modulate the DV for boost control purposes?

Quorb,

This link points to a description of how the N75 regulates boost by controlling the wastegate (from an Audi forum, but it's the same mechanism).

Also, here is a block diagram of a 1.8T engine. It's actually a diagram of a Diamond Star (Mitsubishi/Chrysler) engine, but I haven't been able to spot any differences between it and the VAG 1.8T

The only thing missing off the Diamond Star diagram is the N249 sitting between the inlet vacuum pipe and the DV (BOV on the diagram) plus the vacuum reservoir next to it...

I wonder why there are two separate mechanisms fitted to the 1.8T that can control the boost? I guess "ordinarily" in a turbo engine the wastegate is the boost control and the DV is used for the more classic purpose of opening when off the throttle - but VAG appear to use the DV in a much cleverer - and wear-creating - way don't they ... why oh why I wonder ...

Don't we have any VAG engineers visiting the forums to explain such mysteries to us?

The only thing missing off the Diamond Star diagram is the N249 sitting between the inlet vacuum pipe and the DV (BOV on the diagram) plus the vacuum reservoir next to it...

I wonder why there are two separate mechanisms fitted to the 1.8T that can control the boost? I guess "ordinarily" in a turbo engine the wastegate is the boost control and the DV is used for the more classic purpose of opening when off the throttle - but VAG appear to use the DV in a much cleverer - and wear-creating - way don't they ... why oh why I wonder ...

Don't we have any VAG engineers visiting the forums to explain such mysteries to us?

Hmm, interesting....

Perhaps modulating the DV allows fine control over boost pressure, while still allowing the turbo to spin at useful speed, minimising lag?

The upshot of all this, by the way, is .. I'm fitting a part-used DV from a friend tomorrow in place of mine (he's gone for a Forge on his Leon but is certain his old one is fine - he replaced it "because it might fail" ).

We'll see if it clears the fault. If it does, the warranty can fund a new one. If it doesn't I'll pop the old one back in and Skoda can have a proper look at it for a day or so

Aaaannndddd .... (drumroll please) ....

the part-used DV sorted the problem. It's like driving a different car - well - at least when changing gears. No "fluttering" noise - smooth gearshifts ... sweet. VAGCOM reports no faults and everything is hunky dory!

Now to try and get the dealer to hand over a new DV ...

Phoned the dealer. It was a different bloke than I've been dealing with already so had to explain the whole saga to him again. Told me that I'd have to physically visit them with my warranty docs. Grrr.

So - I drive round there yesterday, faulty DV in hand, plonk it on his desk, explain that I've had some warranty work done and that they utterly failed to diagnose the correct item and that I replaced it with a spare from my mate for the time being - gimme a new one ta (I'll gladly fit it). He explains that they have to book it in on a job card, get the warranty company to order one in, the new one turns up and then I can collect it - IF the warranty company pay for it!

He reckons that a faulty DV on a 3-year-old car could be considered wear and tear so if the new DV turns up and the warranty company won't pay, I'll have to.

F(!"