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Polo 1.4 16v flat vs square lambda sensor


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Hi all, I was hoping my first thread to be me starting with my Polo project, but that needs to wait until I fix my other Polo, for which I need a bit of help as a quick search didn't pan out :(

 

Basically the troublesome Polo has issues with cold start. It starts and cuts off almost immediately. After 5 minutes of struggle to rev it, it manages to stay on, and after a while (as it warms up), there is no problem with starting it again... Starting it directly on LPG also has no issues. So generally I though the petrol pump was bust, but I checked with another one, and there is no difference. The only error it has is about the lambda sensor. It had it way before any issues where presented. At some point the catalytic converter was also removed. The throttle body is also clean and working properly.

 

So as I have another 6n2 Polo with the same engine, I wanted to swap the lambda sensors and check if it would change anything. We only managed to swap the MAP sensors and make sure it is not from them, as the lambda sensors apparently are different.

 

So the question at the moment is why are they different? The troublesome Polo is using a square plug sensor, where the other one is using the way cheaper flat plug sensor :) If I get a flat one for the troublesome Polo and just rewire the plug will it work, as this is normally done with other vehicles, using universal lambda sensors with the existing original wiring?

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Edited by kainy
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Hi One thing not mentioned is the recalibration of the throttle. On the AUA, is it done by  - turn the ignition ON - press the accelerator pedal down to the floor gradually - keep

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nige8021

First Welcome to the forum.

 

The Lambda signal is not used during the start sequence, what you are describing is classic coolant temp sensor problem, it doesn't cause a fault code but if you have VCDS you can see the live data from the sensor, and it makes no difference if the gauge in the speedo is working normally, as the sensor is a dual element unit with one giving info to the ECU and the other to the gauge

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Hmm, I believe this was one of the first guesses the shop had, and they should have swapped the one from the working Polo, but I forgot to ask, if they did it :) I'll check first thing tomorrow, thank you :)

 

This is the one, right?

 

 

TS10279.BMP.jpg

Edited by kainy
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nige8021

Yes that is the correct one but make sure it is a genuine one from VW as ones from autospares shops are not to be trusted the quality is generally very poor, so it might work for a few weeks and then you have to replace it again

 

Correct part number is 059 919 501 A and it should be a Green body  https://volkswagen.7zap.com/en/rdw/polo+derby+vento-ind/po/2001-240/9/919-919040/#7

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Apparently they checked the temp sensor also. But I just remembered that I can cut the lambda on my working Polo and test it on the other ones plug, before buying a new one :)

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The lambda was changed and now the car starts fine and works on idle with no issues. The lambda sensor error is also gone. But the car shuts off imediately or after several “burps” when some throttle is applied. If throttle is applied very slowly at start it will then rev without issues. Once the car warms up a little, it is fine... On Monday we’ll continue investigating the issue. Any ideas will be geatly appreciated :smile: 

 

So far the following was checked, with no issues:

throttle body - cleaned and working fine

temp sensor

fuel pump

MAP sensor

had recent change of oil and filters

had recent issues with leaking head and oil with the spark plugs - fixed, but I’ll check the plugs again on Monday

It has the AUA engine if it matters :smile:

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nige8021
2 hours ago, vwfan3 said:

Hi

Is the accelerator connection to the throttle via a cable ?

 

It's an AUA engine so it will be a drive by wire TB

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It actually had an EPC error, even before this issue was presented, but was resolved, I don’t remember how exactly. I’ll be changing the spark plugs and cables tomorrow (the coil was recently changed), and will see if something changes. If that doesn’t help I’ll have to move the car from the electrical shop to an engine one :smile:

Edited by kainy
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Hi

One thing not mentioned is the recalibration of the throttle. On the AUA, is it done by 

- turn the ignition ON

- press the accelerator pedal down to the floor gradually

- keep it pressed for 5 minutes

- turn ignition OFF

- release the pedal.

 

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nige8021
2 hours ago, vwfan3 said:

Hi

One thing not mentioned is the recalibration of the throttle. On the AUA, is it done by 

- turn the ignition ON

- press the accelerator pedal down to the floor gradually

- keep it pressed for 5 minutes

- turn ignition OFF

- release the pedal.

 

 

This is not the method too recalibrate the throttle, the only way is by using VCDS 

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Both types of adaptation didn’t change anything. The throttle was at 12% before the adaptation and 9.5% after. When the car gets to 40 degrees it throttles with just a small burp in the beginning but doesn’t stall.

 

 

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After several more hours of pointless struggling with the issue, I noticed that the “fixed” head is not so fixed and was leaking from near cylinder 4. Until I fix this, again, I won’t bother with the throttle issue, while secretly hoping it is conected to loss of cylinder pressure :smile:

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  • 5 weeks later...

As I hoped, the issue was resolved once the head was properly fixed. I think only 1 valve lifter needed to be replaced, everything else was seals, gasket and polishing.

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  • 4 weeks later...

1 week later, the oil lamp has came up, my mother continued driving it on the highway, when as a result the engine gave birth to all of its oil :smile: Apparantly the oil pump has stopped working and the engine overheated. Now the car’s future is to be a donor for my old/hers new polo :smile: 

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I want to say that I’m a good son... but I might have been looking for an excuse to change mine with a GTI :pardon:Anyway... the polo is cheap enough for her abusive ways of handling a car :D

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