3.0 TDI CDYA - AGR valve stuck open at 99.6% + RPM fluctuation

Hello everyone,

I have a similar question to one that was already discussed here.
Ich kann den Text nicht übersetzen, da du keinen Text angegeben hast. Ich habe nur einen Link. Bitte gib den Text an, den du übersetzt haben möchtest.
Unfortunately, the topic is locked, so I'm starting a new one.

Briefly, regarding the conditions.
It's an Audi A6 4F 3.0 TDI, manufactured in November 2008, model year 2009.
With CDYA engine and 239 hp, automatic transmission KJC.
The mileage is 195,000 km.
The DPF regenerates regularly.
In principle, there are no unusual findings or error log entries.
I have been driving this vehicle since 2020 (starting at a mileage of 167,000 km), primarily using it as a winter vehicle for long-distance trips, and in the summer, I take it on one long vacation trip each year.
"For the past 2 years, I've been using it daily, even from fall to spring, and also for short trips."

I noticed the following.
Condition: Cold start, temperature around 0°C, start driving and after 200 meters, maintain a constant speed of approximately 50 km/h on a flat surface, with or without cruise control.
It has been observed that when the engine is cold, the RPM fluctuates in a sawtooth pattern by approximately 100 revolutions. This is noticeable for the first 1...2 kilometers, but then it gradually diminishes until it becomes imperceptible.
In the summer or when driving uphill, in city traffic at intersections and traffic lights, or generally when there's a break in constant driving, this isn't noticeable at all; it only becomes apparent when a specific routine for driving home is mentioned.

Based on these observations and a review of many forum posts, I then performed several logging sessions using VCDS.
In the attached log file, there is a record from January 21st at 7:13 PM.
from second 227 to 253, you can see the fluctuation in the speed.
From second 391 to 429, it is almost completely gone.

I've also noticed the following:
The actual boost pressure is often above the target boost pressure (green vs. green-blue).
and the exhaust gas recirculation mass is almost always equal to the total actual air mass (light green vs. brown).
and is therefore usually 300mg/H above the target value for the exhaust gas recirculation air mass (yellow).
and the control of the EGR system is consistently at 99.6% (darker blue), except for two brief moments.

One might suspect that the AGR valve is stuck in the open position and is perhaps reporting that it is "stuck" at 99.6%.
Therefore, I performed the EGR test in the basic settings of the engine control unit and found that it is working perfectly. And there, the control value constantly switches from "AGR not active" at 0% to "AGR active" at 84.4%.
In this process, the actual values of the exhaust gas recirculation also change from approximately 580 mg/h to 311 mg/h, and fall within the specified range. Okay, so with AGR at 0%, 580mg/H passes through the mass airflow sensor, but with AGR at 84.4%, only 311mg/H passes through, because 269mg/H is being added from the AGR system... that's at least how I interpret the test results.

I would be very interested to know if anyone is familiar with these phenomena and can help me understand why this is happening.
Perhaps the AGR (Abgasrückführung) control system, with its 99.6% efficiency, is also related to the "jerking" or "stuttering" issue?
"Anyway, I also did some driving with high RPMs, even into the red zone, and the EGR valve was still fully activated the entire time. According to the basic settings test, it should also remain permanently open."
As far as I could read, the EGR valve should be closed at full load and engine speeds above 3000 RPM, which, according to the control value of 99.6%, it definitely is not.

Best regards.

Hello,

There are many valuable tips in the other topic.
As I understand it, the 99.6% activation of the AGR (Abgasrückführung) occurs when the actual mass airflow rate (MAF) is above the target mass airflow rate, and the target value cannot be reached.

In this case, I would review the other topic again and visually inspect (or disassemble) the possible actuators. Detached flaps/levers, etc.

Best regards, Rainer.

Hello Rainer,
I had read the other topic very carefully and thoroughly several times.
It described a potential issue where the diverter valve in the EGR cooler might be stuck.
However, this can only be seen with a fully installed AGR cooler, as I could interpret from the photo.
Furthermore, the description indicated that the error occurred because the desired EGR value was higher than the actual EGR value.

Neither of those applies to me.
First, the AGR basic settings test shows that the AGR is functioning correctly and is setting and achieving the specified values within the test cycle.
Secondly, according to the KDataScope analysis, the amount of EGR gas being fed into the engine is higher than the target EGR amount. Therefore, based on my interpretation of all the graphs, it seems illogical that more exhaust gases are being recirculated into the engine, and yet the engine control unit (ECU) is constantly commanding it at 99.6%.
Thirdly, the EGR valve is supposed to close under full load.
I'm reading these three facts from the evaluation curves... have I interpreted them correctly?
In the case linked above, it was the opposite, which is why I consider a stuck valve or a clogged EGR pipe to be rather unlikely.
Could it be possible that the vehicle was in a workshop before I acquired it, where an engine control unit (ECU) update was performed, and something went wrong during that process, causing the EGR valve to be constantly activated?
Best regards.

Quote:

First, the AGR basic settings test shows that the AGR is functioning correctly and is setting and achieving the specified values within the test cycle.

No, he doesn't show that. I don't want to put it too harshly, but a 100mg/H difference between the EGR being ON and OFF is not a "predefined value of a test cycle," but rather pure nonsense.

Just like the images and logs, I won't explain everything here, as it's all been documented for years. The search function is your friend.

"If you're willing to actually repair my car, please provide feedback on the mechanical condition of the EGR/throttle system, including the EGR cooler."

dieselschrauber wrote:

First, the EGR basic setting test shows that the EGR system is functioning correctly and is setting and achieving the specified values within the test cycle. Quote: No, he doesn't show that. I don't want to put it too harshly, but a 100mg/H difference between the EGR ON/OFF point is not a "predefined value of a test cycle," but pure nonsense. I don't want to leave it like that. I'm not referring to the 100mg/H difference value shown in the example text within VCDS. but exactly as I wrote in my first post. When performing an active AGR test, hovering the mouse cursor over the fields displays the expected value range, and the displayed values fall within that range. It's also beautifully shown in a video. If you search for "VCDS Talks: Checking the AGR system with VCDS" on YouTube, you will find it. I wrote:

And there, the control value always jumps from 0% when the EGR is not active to 84.4% when the EGR is active.
In this process, the actual values of the exhaust gas recirculation also change from approximately 580 mg/h to 311 mg/h, and fall within the specified range. Okay, so with AGR at 0%, 580mg/H pass through the mass airflow sensor (MAF), but with AGR at 84.4%, only 311mg/H pass through, because 269mg/H from the AGR are being added... that's at least how I interpret the test values.

Quote:

So, I'm seeing a reduction in the amount of fresh air by approximately 47% when the EGR system is activated during the baseline test. You continue to claim that my images and logs are

pure, unadulterated bullshit

Quote:

. I can only apologize for that. I've been using VCDS for almost 10 years now, I also bought my VCDS HEX-V2 from the Dieselschrauber-Shop, and I'm constantly trying to learn more. I tried to record what I considered to be the important data using the log file. The three attached images are intended to illustrate the speed fluctuations and highlight the difference in the first few kilometers when driving at a constant speed. Furthermore, I read the following post in this forum: Creating and preparing VCDS log files for the forum (technical article). Okay, I'm ready. Please provide the German text you want me to translate. and try to adhere to the following:

Therefore, one should log as few Measurement Work Breakdown (MWB) items as possible, but all of them should provide the necessary measurement data for analyzing the specific problem.

Quote:

Therefore, I have recorded the data from sections 3, 8, and 10 of the MWB that are relevant to me. I have a question about the data. When I consider the following measurement modules, I can see that... the EGR valve is fully open. The actual exhaust gas recirculation (EGR) value is higher than the target value and corresponds to the mass airflow sensor (MAF) value. Or does this mean that all mg/H values are measured and evaluated by the LMM (lambda measuring module), and that a fresh air value of 593.4 is expected at the LMM, but due to insufficient exhaust gas recirculation, the fresh air reading is 846, which would suggest that the EGR valve is not allowing any exhaust gas to pass through? The latter, however, seems to be contradicted by the AGR test using VCDS... see

. And there, the control value for AGR always jumps from "AGR not active 0%" to "AGR active 84.4%".
In this process, the actual values of the exhaust gas recirculation also change from approximately 580 mg/h to 311 mg/h, and fall within the specified range. Okay, so with AGR at 0%, 580mg/H pass through the mass airflow sensor (MAF), but with AGR at 84.4%, only 311mg/H pass through, because 269mg/H from the AGR are being added... that's at least how I interpret the test values.

Quote:

Or am I fundamentally mistaken in my thinking? I am very grateful for any suggestions. Okay, ich bin bereit. Gib mir den Text. Brand: 231.93 Exhaust gas recirculation target value: 593.4 Exhaust gas recirculation (EGR) target value: 846.0 Exhaust gas recirculation control 99.6 Air mass value: 840.1 Motor speed G28: 1764. Exhaust gas recirculation feedback -0.8 Air mass flow rate: -0.1 Thank you very much.

Quote:

The actual exhaust gas recirculation rate is higher than the target value and corresponds to the mass airflow sensor value.

In all cases, it refers to the mass of air drawn in, and the term is poorly chosen because it describes the intended application rather than the measured value itself.

PS: If images are intended to document a specific situation, they should be named accordingly, rather than with generic filenames like "Image_20250228_222827.jpg". There is also a field for a description.

Otherwise, I will send you "3ab-47-11.jpg" with 8 colored curves as my future response.

1. Understand the measurements and don't just record everything randomly.
2. Understand what you want to determine, define the goal of the action, and identify the operating conditions required for it.
3. Record only what is necessary.
4. Name everything appropriately.
5. Question and evaluate all (!) claims, regardless of where they appear (e.g., in diagnostic programs, posts, etc.), to determine whether a given statement is accurate and why or why not.

The absurdity begins with the recording of redundant or unnecessary values, which indicates that either no thought was given to the intended purpose of the recording, or that the person responsible was incapable of considering it.