Polo 1.4 16v engine light and rough running

[AJB]

Hi all,

A friend has a 2000 VW Polo (6N2 type) with the 1.4 16v engine. For a while it has been intermittently putting one or the other of its check engine lights on, and running roughly, especially at lower revs.

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

I had a look at it yesterday 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

[walksy]

I have the same problem. I spent a few £ on getting Lamder sensors changed, it fixed the poor running but the management light has a mind of its own!
If you can live with the light being on you can give it a try.

Also I use fuel additives like Redex, it turns the light off after a few bottles worth.

My next step is disconnecting the dam light as the car is running fine

[Crasher]

Well I don't know which engine code the car has but I would say either a lambda sensor fault or the EGR valve sticking open if it has one.

[AJB]

I'm afraid I don't know the engine code... It's a 1.4 16v about 2000 model year.

It does have an EGR valve. It seems to just have one metal pipe from the EGR valve to the throttle body, and a short stub of vacuum hose to a valve of some sort that vents to atmosphere. There isn't a separate vacuum pipe going to the inlet manifold as far as I can see. The electrical connection is on the top of the metal body of the valve.

It is gently sucking air into that stub of hose whilst idling (you can feel it if you block the end with your finger, but it's slight enough that you can't hear hissing or anything). Is that normal?

How would I check whether the EGR valve is sticking?

Thanks for your time,

Alan

[Crasher]

PM sent.

[AJB]

One more bit of info - I think from something she said that the revs sometimes hunt a bit when it's idling.

On old carb engines, I seem to remember that that's often a sign that it's running lean, which would go with the additive fuel trim fault code I've got...

That made me think that it might not be the Lambda sensor though - if that was faulty, and reporting that it was too lean even though it wasn't (giving the too lean fault code I'm seeing), then I'd expect the ECU to be adding too much fuel to try to get the faulty sensor to report correct mixture. So I think if anything I'd expect that to make it run too rich along with a "too lean" fault code.

But then hunting might not have anything to do with mixture these days...

Crasher: Thank you - email sent!

Also, does anyone have any feel for whether an air leak between the air filter and the throttle body could be causing the problems? My Skoda Octavia Haynes manual (which includes a 1.4 16v) says that it's "most important" that this makes an airtight seal, but it doesn't say why or what happens if it doesn't. Without a MAF sensor, I can't quite see why it would matter if a bit more air got in there, before the throttle butterfly... A bit of oil has leaked out of that join though, and so I guess air might be getting in...

[Crasher]

The other possibility is (according to engine code) a cracked plastic inlet manifold.

[AJB]

Whereabouts does it crack? Would I be able to see a crack if I take the air filter housing off and look down on it from above?

Thanks yet again!

Alan

[Crasher]

They crack anywhere there is a seam for the two halves.

[AJB]

In case it's useful to anyone else, it's actually a 2001 model, with an AUA engine. So much for my helpful "2000 VW Polo" in my original post!

And thank you Crasher for all your help!!!