2.0 FSI Poor idle when cold

[MEL744]

Interesting read, definitely clears up a lot. I've been looking through the logs and I'm not convinced the label file is correct when it comes to values associated with the cat temp. In measuring block 43, the Catalytic Converter Bank 1 Temp varies from 12-150c, while in measuring block 46 it varies from 12-60c on the same start. Then in block 34 on a different start it varies from 12-714c. This makes me question whether the Lambda labels are correct as well. The supposed Lambda sensor values don't really seem to change with time. They remain constant at about 0.44V on Bank 1 and 0.435V for Bank 2, which would indicate a slightly lean mixture according to some data I have found on Lambda sensors. (0.45 - 0.5V apparently corresponds to stoichiometric air/fuel ratio).

[saabman]

The information in the Label files does seem to be a bit vauge and "best guess" with the amount of variations in VW engines Im not surprised no one can really hit it on the head ...

I was watching a youtube video about Fuel trim at lunch time today YouTube
and from what I could gather from that the voltages from the O2 sensor should remain pretty well steady ( should oscillate around 0.45V ) if the they sense a richer mixture the ecu should reduce the injector timing if the sense lean the ecu should increase injector time this would be seen as a variation of the fuel trim values. The ECU should be doing everything it can to keep the O2 sensor values constant. There are times it should vary like when accelerating or decelerating.

[MEL744]

Alright so from what VCDS is telling me, there is no oscillation whatsoever. It just stays on 0.44V or 0.435V, based on how the engine should be reacting there should be the oscillation in voltages from 0.1 to 0.9V. I am not sure if it is displaying a constant voltage because it is cold (can it even reach operating temperature in 30 seconds with heating?) or it is broken. Will try to make a log of the voltage when driving around today. Have also found that the second O2 sensor is downstream of the cat and used to compare O2 content after the exhaust has been through the cat, in order to check whether it is working properly.

[saabman]

I think your right about it not reacting because its cold. i dont have a log of the actual o2 sensor voltages but have Group 1 values which are the Lambda control values - Im assuming this is the calculated raw trim value to be applied. I have 2 lambda sensors 1 for cylinders 1 & 2 and 1 for cylinders 3 & 4 you can see in the graph there is nothing from them for 30seconds and then they start producing a signal that signal is then not applied to the fuel trim values for another 10 seconds

[saabman]

Given the current readings from the O2 sensors dont have an effect on the running of the car at start up Im wondering if there is something occuring when the engine is hot and that is pushing the trim values right out, thta figgure is stored and used as the start up value but is not right for the condition of the engine at that time -and the engine runs like crap untill the o2 sensor values kick in?

Apparently clearing engine fault codes resets the fuel trim values - I wonder if clearing the codes prior to a cold start makes a difference? Unfortunatley I cant try this out as my daughter lives 200km away so I can only work on the data I have - I might have to send her up my HEX-can cable (over my dead body LOL) I should see if the light version will do logging...

[saabman]

Heres the Trim values v RPM you can clearly see as soon as the o2 sensor values are applied to the engine starts running right

[JustCruisn]

So is this saying the O2 heaters are not working ?

[MEL744]

stored and used as the start up value but is not right for the condition of the engine at that time

This sounds very reasonable. Seems to be using some fixed value, would potentially explain why it runs fine if you restart it - it calculates a new value or maybe the heaters have more time to work?

Apparently clearing engine fault codes resets the fuel trim values - I wonder if clearing the codes prior to a cold start makes a difference?

I reset a check engine light the other day - I don't recall it making a difference but will retry it any pay more attention.

Unfortunatley I cant try this out as my daughter lives 200km away so I can only work on the data I have

Let me know if there are any values you'd think would be particularly interesting to log and I'll get them

So is this saying the O2 heaters are not working ?

Maybe, but they might be working fine, I'm not entirely sure how quickly they should heat up. You also seem to have the 2.0 FSI, do you have this rough start condition?

[MEL744]

Made a few plots related to the Lambda values today. This was from a cold start and I drove it until it came up to temperature on the dash - however nothing much interesting happens after 5 mins so I truncated the data there. The vertical red line represents when the rough idle period ends. Plot is available here (recommend downloading and viewing on your computer as Google Drive viewer isn't the best).

[saabman]

That looks great.
A picture certainly tells a thousand words ...

The readings from Bank 1 seem to be all over the shop while bank 2 is reasonably consistent . On mine its bank 2 that is all over the place and 1 is more constant. is it the sensor or is it something else

I come across this tonight which might help.
http://www.vaglinks.com/Docs/Audi/B5...r_Checking.pdf