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Author Topic: 1.8T 2003 GTI Lambda values oscilate from 0.8 to 1.3 at idle.  (Read 3732 times)
Parati
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Hello guys, my GTI is weird after I cleaned the O2 sensors connectors. At first, it was really rich at idle, like 0,65-0,7 lambda (I have an Aftermarket O2 reader installed). Now that I simply disconnected and reconnected the O2 sensors it barely can idle after it is warmed up. The car is far from stock, with a custom remap and catless downpipe. Also, the after-cat O2 sensor is malfunctioning and giving DTCs. The weird part is that the Additive and Multiplicative Lambda correction values are stuck at 0 when logged with VCDS. The front O2 sensor is reading accurately, but the car does not correct values. I wonder what is happening. Would a bad after cat O2 sensor cause this? I'll post here the log file to show how the O2 sensor reading oscillates on idle and how the Lambda correction is stuck at 0. If anyone could shine a light on this problem, I'd be very thankful. If I let any information unknown let me know. I also have the .BIN file for my map, so I might answer tune-specific questions.
Why would the ECU not be doing closed-loop corrections? The car tries to stay at idle, but then Lambda goes to 1.3, so it enriches and this keeps going in a cycle

PS: I've replaced my MAF sensor, so dismiss the error code.
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prj
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« Reply #1 on: March 20, 2021, 12:30:08 PM »

Probably because you have a massive boost leak in the intake?
Why else would you have MAF error.

And then a custom tune where msdk is not calibrated correctly.
So as soon as it switches to the alt load model, you're mega lean.

Put the laptop and internet away and do a boost leak test.
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Parati
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« Reply #2 on: March 20, 2021, 12:34:48 PM »

Thanks for the tips. The MAF error have been fixed, I got a new MAF sensor. I'll try the boost leak check
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Parati
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« Reply #3 on: March 20, 2021, 07:52:28 PM »

Probably because you have a massive boost leak in the intake?

But the car runs fine, even has boost under throttle, the only problem is at idle, that is the weird part. Could it be a vacuum leak?
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prj
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« Reply #4 on: March 21, 2021, 06:36:09 AM »

Pressure test the entire intake from the turbo inlet without disconnecting anything, and you will find out.
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Parati
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« Reply #5 on: April 05, 2021, 05:22:20 PM »

So, I've tested for leaks and found none. I would also add that when I start the car, it works fine for 15 seconds, stable idle and no surges, than it beggin doing the weird stuff. I also have -0.8 bar of vacuum when the car is running fine. Could it be any other thing? It looks like this only happens when the closed loop from the O2 beggins to work.
« Last Edit: April 05, 2021, 05:26:28 PM by Parati » Logged
Parati
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« Reply #6 on: April 05, 2021, 05:37:13 PM »

Here is a LOG showing how the O2 adaptation keeps changing like crazy
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