Hi all,

I'm trying to fix a friend's VW Polo. I've posted this on a VW forum, but had no replies at all so thought I'd post here as you guys are always great when I need help with my Octavia. It's actually a 2000 Polo (so the generation before the 1st Fabia), but it's the same engine...

For quite a while her car has been occasionally putting one or the other of its check engine lights on, and running roughly, especially at lower revs. It's been gradually getting more frequent, and now the lights are on most of the time.

I've scanned it for fault codes, and the only relevant one seems to be 17559 - fuel trim additive air too lean.

I had a look under the bonnet on Monday evening hoping to find an obvious air leak, but couldn't see anything. One thing I did notice, though, is that some oil has been leaking out of the join between the air filter housing and the throttle body. I guess this could mean that air was leaking in there. Would this cause a problem, though? I kind of feel that it won't, as I don't think there's a MAF sensor, so I guess it's measuring manifold pressure instead, and so I don't imagine it would matter how much pressure drops across the air filter. I'm hoping I'm wrong, though, and that's the problem! Has anyone got any experience of that?

If that's not it, is there anything else I should look out for. A VW dealer has already charged her £70 to say that they can't tell what's wrong, so I want to help out if I can.

Thanks very much,

Alan

Rough running is often down to a faulty coolant temperature sensor, although this is usually revealed by the temperature gauge sticking at 0 from time to time. You may want to ask your friend if she'd noticed this, but certainly my wife didn't notice when hers was playing up (read as much or as little into that as you will! :P )

From what you're saying about the oil, though, it sounds possibly as if the breather tubes are clogged. Is there mayonnaise anywhere? It may just be a case of giving everything that's got oiled-up a good clean and then giving the car a good blast to blow away the cobwebs!

How rough is it running?

The management light and EPC lights come on my cousins Furby (1.4 16v) when he goes over a bump and he's going to have that checked at a Skoda place as we dont have the means to read the fault computer.

Have you tried Injector Cleaner?

If there is a leak then thats not good. Has the oil level been dropping more than the usual oil consumption level?

Fuel trim too lean suggests an air leak to me. The time-honoured way to check was to spray plus-gas or wd40 around suspect areas (inlet manifold joints, for example) with the engine running, and it would draw the spray in instead of air, and the engine note would change.Not sure how wise that is with a cat though.

Thanks for all those replies - I knew this was the right place to ask!

I don't think it's coolant temperature sensor, as that gave a fault code on my Octavia, and this one doesn't have any fault codes to do with sensors.

There didn't seem to be any mayonnaise anywhere. The oil leak I was talking about if from where the "oily" side of the air filter (ie the side that gets oily air up from the breather system) joins onto the throttle body. Oily air is meant to get burnt, but some of the oil that's deposited on the air filter housing seems to have been able to leak out onto the outside of the throttle body.

I guess that means that air could leak in there, but my question really is whether a leak there could cause problems. I can see that a leak the other side of the throttle could mess things up, or a leak after the MAF sensor on an engine that has one, but I couldn't see why it would cause a problem on this one. The Haynes manual for my Octavia does say that it's "most important" that that seal is good on the 1.4, but it doesn't say why. I don't know if it's just to avoid unfiltered air getting into the engine, or whether it messes up the mixture too.

In answer to how rough it's running, I'm not sure as it's a friend's car and I've never experienced it. From what she's said, though, I took it to be that it was misfiring from time to time.

Thanks again for your time guys,

Alan

Thats the code I had on my fabia 16v 1.4 when the piston rings went!

If you can see oil dribbling from the air filter housing i'd take it off and have a look inside and at the throttle body as that sounds like it needs cleaning up anyway.

Can anyone say if it is this oil blown up the crankcase breather that causes the rings to go? does this lower the octane of the fuel causing pre ignition and the damage perhaps?

or is the oil/vapour blow up because of the fault or unrelated?

Would fitting an oil catcher or an inline filter be a good idea?

Hope it's not the piston rings..... That wouldn't be good....

There is quite a bit of oily film in the air filter housing on the left hand side of the car (ie the throttle side), but the actual throttle body, and certainly the butterfly, looked oil free.

I'd assumed that that some oil in the filter housing was normal as oily air would come in through the breather... Is it normal?

In answer to whether oil causes the ring to go, no. It's the other way round. If the rings have gone then more exhaust gas will be escaping from the cylinders, past the piston rings and into the crankcase than there should be. There will always be some gas getting past, even if the rings are perfect, and that's why there's a crankcase breather to suck this (oily) gas up and into the engine to burn it, rather than just letting it out into the atmosphere. So, if the rings have gone then a lot more oily gas will be coming up through the breather system. I guess in extreme cases the oily air could contaminate sensors, block up the throttle body, or even foul spark plugs, but it wouldn't be able to damage piston rings.

There will be some sort of an oil trap in the breather system anyway. I think that in that engine, the breather coming up into the air filter comes out of an oil separator box thing which tries to send as much as possible of the oil back into the sump with just the slightly oily gasses getting up into the air filter.

My cousin has had Skoda read the computer and reset it and the lights came back on.

He said

1st prob - 17953, P1545, 035

Throttle valve control system Malfunction sporadic

2nd Prob - 17550, P1142, 035

Load detection - Value below lower limit - Sporadic

3rd Prob - 18081, P1673, 035

Speed Signal Malfunction message from ABS control module - sporadic

But the car runs and drives OK.

AJB,

I thought I would have another look in the engine cover and you're right there is an filter in there for the breather. I thought it was an empty pipe but it has filter in it. I changed the air filter, wouldn't mind changing that too actually.

Sisko, to my untrained mind looks like the first 2 relate to the throttle body, does it look slimey when you remove the engine cover?

I have no idea as I haven't looked .

The engine management light on my uncles Corsa lit up and they had to clean the throttle body and reset the sensor on it.

A garage a said the same thing needs to be done on my cousins Furby a £10 job.

Hopefully that should cure it.

AJB,

Did you ever get a solution to or an explanation of the 17559 error?

A friend of mine appears to have the same problem where the workshop are replacing the car bit by bit but the problem keeps reappearing after about 200 km. In this case it is a 1,4 16V in a Fabia 2001.