Stuttering 1.8T when moving off

[pearce_jj]

Hi all

Been ages since I posted last, I must appologise

Anyway my 04 Mk.I Octavia 1.8t auto is a bit sick. When pulling away from a standard start gently (I do mean a normal pull-away, not fast) when the engine is cold, occasionally:

- initially fine, engine spins on torque converter to maybe 1800rpm as usual
- power builds as torque converter is closed to a sudden burst, way in excess of throttle position calls for,
- almost immediately the power is removed entirely for ~1s
- then it works normally.

I first noted this with my dealer last year (under warantee), but they couldn't find anything.

Now it has got to the point of being dangerous or at least disconcerting. Its is surging to full throttle plus, which when your edging out of a side junction normally is not good!

Any and all ideas very much appreciated. It's at the dealer today but they don't sound very confident. Auto box seems otherwise fine, fluid was changed last year (after I'd first noted the problem), full history, 30k on the clock. Fuel consumption is about the same as always, a disspointing 30mpg. Performance is otherwise OK, no errors reported on screen.

I have read the dump valve can stick, which sounds plausible to me, the auto 'box meaning the engine is spinning right on the point of boost.

Thanks
James.

[RichB86]

i think a few people have this when cold i usually find let it idle a few mins then restart stops it.

[Bodge]

yep ive had this loads of times. so i recon its not your auto box at fault.

have you done a fault code scan? would be interesting if the 17705 code came up (pressure drop between DV and throttle body). as i have this.

i've recently changed the N249 valve (which is the electronically actuated valve sitting under the intake manifold that controls the dump valve). i only changed it last week, so i cant be sure yet, but the problem seems to have gone away.

if its the same as me, then it feels like a sudden but short dip in power, but otherwise fine. gets a bit annoying for the neck!

[pearce_jj]

Hi, thanks for the replies gents. I don't think the 'box is at fault, just that its accenuated by it because it lets the engine spin to turbo-spool speeds by default.

The sensor is interesting. Garage said there were no fault codes but are keeping it overnight to look at tomorrow. God knows how much this is going to cost me!!!

It does feel like a sudden dip, but only after a sudden peak. Possibly because of the auto, the peak might easily be not noticed in a manual as you'd be slipping the clutch when it happened, if it's the same as mine.

Anyway, thank you for taking the time to reply, much appreciated.

Thanks
James.

[Bodge]

that definately sounds like the same problem there.

ask them about the N249 valve, and see what they think.

i have part numbers, prices and diagrams if you need them buddy.

keep us posted on how things go....

[pearce_jj]

Hi,

Not got much further. Nothing on diags and dealer not able to reproduce it. But I know it's not my rubbish driving, because my wife seperately commented on it (I didn't mention it to her first).

Apparently there is a tech advisory on this exact behaviour and the dump valve is the cause, but it's only for when it is experienced at temperatures below freezing

So basically £150 so far an no progress other than a cleaned throttle body

Thanks for the help thus far.

[fatty5000]

Just wait about 1 minute before trying to drive away.


Works for most people



HTH

[kirk]

I am also seeing this with a cold motor on a '04 RS. I just bought and it's one of the first features i noticed with it. Otherwise it works just fine.

So this is something that is normal then?
There is nothing that can be done to it?

Is there some other possible culprit than the N249 valve?

[fatty5000]

It is something a lot of people experience, mine used to do it, though why it stopped I have no idea, I used to let it run until the secondry air pump stopped, then I tried using it with out waiting once or twice and it seems to have stopped doing it these days.

I wouldn't go so far as to say it runs perfect when cold but it certainly ain't is or has been as bad some people describe in my experience.
But I do think that it is a trait of the engine that is a bit hit or miss.


HTH

[pearce_jj]

I'm currently exploring the N75 valve route. This, to my mind, is the most logical. Anyway I've asked the garage to just price replacing both valves and the DV, although they don't seem keen to give me the number

[fatty5000]

Seriously, have you tried not driving it until the secondry air pump has stopped doing it's thing ???

[pearce_jj]

it does it now occasionally when warm to - 7 miles or more.

But it is more often when cold I admit. Frankly the surge can be so agressive it's quite dangerious on reflection. Say I was pulling out behind a cyclist...

[fatty5000]

Sounds like more than the "normal issue" then tbh.

N249 could be a good place to start looking as you say

[pdhealy]

I have had similar symptoms - no fault codes. I tried cleaning the throttle body, and this helped.

[pearce_jj]

interesting, that's what the garage has just done. Will see how it drives when I get it back although they did say it wasn't grimey anyway.

[lordrobs]

Originally Posted by fatty5000

It is something a lot of people experience, mine used to do it, though why it stopped I have no idea, I used to let it run until the secondry air pump stopped,

Mine is as rough as a badgers backside when the secondary air pump is running. Its fine the rest of the time so I ignore it

[Bodge]

i think we're getting confused here!

2 different issues are being discussed:

-cold start lumpyness/bad running (which could be fixed with a new air temp sensor in the inlet manifold, or just let the secondary air pump finish its business before driving)

-and the pulling away sudden and quick boost drop (which could be solved by N249 I recon, or N75)

With the cold start engine lumpyness/poor running, you might fix it easily, like i did, with replacing the old oil/dirt covered air temp sensor with a nice new one.

a new N249 seems to have fixed the sudden boost drop thing aswell for me. that symptom didnt care if the engine was hot or cold with me, it just always did it. my neck is much better now!havent touched the N75, so could look at that first if its cheaper, and its definately easier to change!

[pearce_jj]

Thanks All!

Here's the parts costs -

N75 - £57+vat part, £86 fitted incl
N249 - £21+vat part, £87 fitted incl
DV - £18+vat part, £83 fitted incl

Although I found an N75H (OEM part?) for £40inc elsewhere.

Are these all DIY'able? DV in particular looks very expensive for a what appears to be a 10 minute job.

Thanks,
James.

[Bodge]

DIY it mate.

-DV is very easy
-N249 is awkward but not hard, just takes patience
-N75 looks easy but ive not tried

Part prices look good there, Skoda charged me £40ish for the N249, and DV was £100 (Forge admittedly!!)

[pearce_jj]

Thanks, anyone got a page from a haynes manual on this area they could scan?