Misfires at Low RPM and Light Load

Hello everyone,

"My Passat TDI has been acting up lately, and I'm not sure how to pinpoint the problem. (1.9 TDI, PD, first registered in March 2000, engine code: ATJ, 340,000 km, chipped for 12 years / 200,000 km)."

It started about half a year ago when he started having problems, specifically a misfire, in a tight turn that I drive every day.
"For about 3 months, the misfires have become more frequent and have recently started occurring almost every time I drive. They are irregular misfires that occur at low speeds or low load, and only at engine speeds below 1600 RPM. This is typical driving in the city."

Right after starting, everything seems fine, but after about 10 minutes of driving, when it starts to warm up, that's when the problem begins.
Under high loads or at higher speeds, such as on the highway or country roads, it runs normally and delivers full power.

So far, the following has been done:
Error memory read multiple times: no entries found.
Fuel filter replaced.
Air filter replaced.
PD cable harness replaced.
LMM temporarily replaced with a diode for testing.

"So far, no success. Since replacing the power distribution cable harness, the effect seems to have gotten worse. Now, I'm also experiencing an unstable idle occasionally. I don't see a direct connection, but maybe I accidentally touched or moved something while working on it. I'm leaning towards ruling out the tandem pump, as it seems to work fine at high RPMs and under load."

How should I proceed with further troubleshooting?
Can I rule out that the effect is caused by, for example, ESP or ABS? (Turning off ESP makes no difference).
Could it be coming from any sensor, such as the throttle position sensor, or something similar? (I seem to recall that when I release the accelerator, there's sometimes a slight jolt that wasn't there before).
Which other sensor could potentially cause a similar effect (e.g., intake manifold pressure/temperature)?
Should I read out specific values or post them here?
VCDS is not always available, but I might be able to borrow it next week.

I would appreciate it if someone could help me here.
Perhaps there's someone here from the BGL or TS region who is knowledgeable about the technology.

Greetings.
Rupert.

Hi Karli!

The PD cable harness would have been my first suspect in this case, but it has already been replaced.
The next step would be to take a look at the EGR valve, as it's likely to be quite dirty and worn out after being used for so long.

Regarding those "mistakes" again:
Sind die eher richtig "hart" oder eher wie so 0,5sec. verzögerte Gasannahme z. B.?
And does the engine start smoothly without any misfires or stutters?

The most helpful thing to do right now would be to create a log with the following parameters: 13, 18, and 23, both in a cold state and a warm state, while idling for several minutes.
This could provide some insight into PD defects and/or seals.
And don't forget the Autoscan!

Best regards from Munich!

Hello DieselBär,

Thank you for the quick response.
AGR has had a "closed" system for 12 years...
I'll check it out tomorrow to see if there's anything wrong with it, even if it seems okay now.

The cold start is perfect, and the first few minutes of driving are also fine.
The jerks are quite noticeable, especially in second gear when driving in the city, as there's a real jolt that goes through the car.
So, there's no delayed gas intake. Typically, it's more often the other way around, meaning it starts normally for the first 0.5 seconds, and then there's the interruption.

I should be getting the VCDS next Tuesday, but I'm not very familiar with it. It's possible that I might have to ask some basic questions then.

Best regards from Bad Reichenhall.

Hello Dieselbear,

I've just taken a look at the MWBs.
I wasn't able to display the graphs, so I only have instantaneous values. However, I observed the warm and cold values for several minutes each. They only fluctuate minimally.
I also ran an Autoscan. It showed some errors, but I don't see any connection between those errors and the misfires.

Please review the values and see if anything seems unusual.

For a while, I even tried leaving the gas cap off, but that didn't have any effect either. The frequency of the misfires varies greatly, so it's hard to tell if any particular measure actually makes a difference.

Als nächstes hätt ich mir durchsichtige Spritleitungen besorgt und mal nach Luftblasen gesucht. WWhat do you mean?

Regards,
Rupert.

Hi Karli!

Thank you for your current values, but this is NOT a LOG .

Please record the data again for a period of 1-2 minutes, once after a cold start (allowing the engine to cool down for at least overnight!) and once when the engine is warm, as I mentioned before.
Individual values have no significance here, as we would like to observe the general behavior of the VAT law over time.

We use Autoscan so that we can see and assess the installed components, their coding, software versions, and other relevant information.

Best regards from Munich!

Yes, I know that's not a log.
But I couldn't get it to work. I can access the diagram, but nothing is displayed (even though the checkbox is ticked), and nothing is being recorded. What am I doing wrong?

Greetings.
Rupert.

Hi again!

First of all: Your version is (very) outdated. The current version is 15.7 (4).
Please update this to the version mentioned above, or have the owner do it (also in their best interest).

Please run the Autoscan again and upload the results here.

There is a technical article about the Log's.
/viewtopic.php?t=12979&highlight=log

Otherwise, select "StGe" -> "01 Motor" -> "Measurement Blocks" -> enter the values 013, 018, and 023 from top to bottom into the respective front fields and confirm with "Enter". Then, there's a button at the bottom labeled "Log" (or something similar - I don't remember the exact wording). Clicking it will bring up a window with a suggested file name and save location. Confirm with "OK", and the logging process will start.
You should perform the above procedure with the ignition turned ON, and ONLY start the engine once the LOG is running (!!).

Please translate the following text from German to English, providing only the translation, without any explanations.

Best regards from Munich!

@karlstein12: Unfortunately, you are not a customer. You can find original diagnostic systems in the Dieselschrauber online store, or you can purchase a support key.

Regards, Rainer.
Kaufmann Automotive GmbH
Official distributor for VCDS.