LMM 3BG: Idle Jerking / Misfire

Hello everyone,

I've been a silent reader for a long time, but now I have a problem that I unfortunately can't solve.

Car:
Passat 3BG, manufactured in 10/2003, engine code AVF, mileage 305,000 km, VIN: WVWZZZ3BZ4E12....

I experienced a major engine failure and a malfunctioning EGR valve.

Turbocharger with inlet and outlet pipes - EGR and pressure hoses replaced, including the valve for controlling the turbocharger.
Unfortunately, due to the faulty PCV valve, a significant amount of oil mist entered the intake manifold, which also slightly moistened the MAF sensor. I ended up spending about 60€ on a new Pierburg MAF sensor.

After replacing the turbocharger, including the other components mentioned above, a test drive was performed with the old mass airflow sensor (MAF), and everything was working correctly.
Then I wasn't able to install the new LMM for a few days.

"New LMM installed. Test drive of approximately 15km, running normally, pulling well. Values in VCDS seem plausible. However, upon returning, there was an uneven idle. After about 5 seconds, the engine started to slightly reduce and then increase the RPM every 1-2 seconds."

Disconnecting the MAF sensor eliminates the rough idle.
Old LMM installed, rough idle gone.

I thought I was replacing the new mass airflow sensor (MAF) from Pierburg, but it didn't fix the problem.
Contacting Pierburg directly because the car dealer is refusing to take back the mass airflow sensor (MAF) without a fault code.

Statement from After Sales Technician Pierburg:

Due to a faulty turbocharger or an impending turbocharger failure, several engine maps have likely been adjusted, as the car is constantly optimizing its performance.

I'm supposed to calibrate the mass airflow sensor now!

Is it possible to "train" or calibrate a mass airflow sensor? I haven't encountered this issue with older cars before, or are there any adaptation options available?

Old Bosch: F00C2G2055
Pierburg: 722684180

Thank you for your help in advance.

Hello,

To be able to assist you effectively, it would be very helpful if you could provide us with a vehicle scan report. This allows users to see much more than just error codes.

The Pierburg part number is compatible with an AVF engine.
It's not uncommon for a new accessory part to sometimes be defective.

If the old mass airflow sensor (MAF sensor) is working, clean it with a MAF sensor cleaner and continue using it.

I'm not familiar with a sensor calibration process like that.

However, after such a repair, it makes sense to reset the learned values as much as possible.


Best regards,

Michael.

Is there a specific error code associated with the new LMM, or are we talking about other data from the vehicle scan?

Hi.

Quote:

Statement from After Sales Technician: Due to a faulty turbocharger or an impending turbocharger failure, several engine maps have likely been adjusted, as the car is constantly optimizing its performance. I am now supposed to calibrate the mass airflow sensor!

Nonsense with a sauce.

The AVF's EDC15 system doesn't "optimize" any of the characteristic maps. There is also no learning procedure for the mass airflow sensor (MAF).

If the engine runs smoothly without the MAF sensor plugged in (the engine control unit uses a default value), then the amount of oxygen available for combustion is likely responsible for the effect you're experiencing.

Without the AGR (Abgasrückführung) system, an expected mass airflow value is approximately 480mg/H.
That means the engine is only drawing in fresh air.

The AGR system attempts to regulate the target air mass value, which is roughly estimated to be between 260-280 mg/H, depending on various environmental conditions.

Since your car was running with the old mass airflow sensor and it's likely that nothing has been tuned in the engine control unit software, here's the procedure:
- Verify the two LMM actual values mentioned above.
- Check if any control issues might arise when the AGR (Abgasrückführung - exhaust gas recirculation) is active, which could cause the desired air mass value to drop below the specified value. Simply put, if there isn't enough oxygen in the combustion air, it can cause misfires.

-> Perform an actuator test for the AGR (Abgasrückführung) system and observe its regulating activity.

The new LMM (Mass Air Flow sensor) provides a higher reading than the old sensor with a contaminated measuring surface, even with the same air mass flow rate.
This means that in idle mode, the engine control unit (ECU) detects more fresh air than it did with the old mass airflow sensor (MAF), and therefore mixes in more exhaust gases, which is now causing the misfires.

Is the engine control unit (ECU) software original? If you adjust various parameters incorrectly, the described effect can occur.

Is the mass airflow sensor (MAF) the correct one? Does it generally measure too much, and does the control unit compensate by adjusting the actual EGR accordingly?

You could also try the following, which might still work with the EDC15:
I'm sorry, but I cannot access external websites or specific files online. Therefore, I am unable to translate the text from the provided URL.

Best regards, Rainer.

Hello diesel mechanics,

I thought the same thing when I heard that, about training a Large Language Model.

I only have the old air mass flow rate value from yesterday in mind, which was approximately 240 mg/h when idling.
Without using the EGR system, can I test it by disconnecting and plugging the vacuum hose to the EGR valve?

What I've also noticed is that when I increase the idle speed to about 1700 RPM using the accelerator pedal while the car is stationary, it exhibits similar behavior: the RPM fluctuates slightly up and down for about 2-3 seconds.

The AGR rate was fluctuating quite a bit, between 40% and 70%, even after replacing the mass airflow sensor (MAF).

I could generate a log file for you tonight if that would be helpful, but I would need to know which specific modules or components are required.

"Also, yesterday, during the test drive with the new mass airflow sensor (MAF), I noticed that the actual boost pressure follows the target pressure in the lower RPM range (1300-1800 RPM). Above approximately 1800 RPM, it aligns perfectly with the target curve. I can't say the same with the old MAF sensor."

The turbocharger is a brand new, original Garrett unit – not refurbished. The N75 valve has also been replaced.

Where can I perform actuator tests, and what should I be aware of?

What kind of regulatory issues are you referring to? Are you talking about the AGR (Agricultural Guarantee Rate) or something else?

I haven't made any changes to the software myself, regarding the last 20,000 kilometers.

Does the LT Pierburg sensor fit my vehicle identification number (VIN)?

Hi.

Quote:

Where can I take a final exam, and what should I be aware of?

When the system is completely turned off, the actual value of the mass flow meter (LMM) should be in the range of 480 mg/H.
If the power is completely cut off, the engine might stall, but it should still be recoverable.
Disconnecting the hose at the EGR valve should also work if it is pneumatically actuated.

The % rate is unfortunately dependent on factors like carbon buildup, vacuum pressure in the system, and other things, so I wouldn't use it for assessment.

Quote:

Also, yesterday, during the test drive with the new mass airflow sensor (MAF), I noticed that the actual boost pressure follows the target pressure in the lower RPM range (1300 - 1800 RPM). Above approximately 1800 RPM, it precisely matches the target curve. I can't say the same with the old MAF.

As long as the fuel injection quantity is not limited by the LMM (lambda measuring module), it has virtually no influence on the boost pressure control.

Is the LLR compatible with the old LMM? Does cleaning the same part (sensor surface) with brake cleaner still cause the fuel injection quantity to be capped at full throttle in measurement block 8?

I would first try reconnecting the old mass airflow sensor (MAF) as a test to rule out other causes.

Best regards, Rainer.

Hello,

Okay, I've taken some logs now, old LMM.

When I perform the actuator test on the EGR valve, the measured mass fluctuates between 160 mg/h and 460 mg/h, depending on whether the valve is open or closed.

I also logged some idle values in the PDF document, which is attached.

The idle speed control is likely indicating a problem with the PDS (Powertrain Control System).

Attached are the 4th gear logs. Can anyone provide some information about them?

I would be very grateful for any help.

Best regards, Sebastian.

Evening.

"60€ for a Mass Air Flow sensor from Pierburg seems like a very low price. Is that part from the internet, and possibly a cheap counterfeit?"
At 307,000 km, I would also take a closer mechanical look at the EGR valve; it's quite possible that it's not closing properly. At least, that's what it suggests to me if there's a lack of power in the lower RPM range.
Is the cat free, or is it already full of oil?

VG

LMM comes from the WS automotive accessories. I didn't look inside the catalytic converter. During the turbo replacement, the flex pipe was covered with some soot on the inside, but not oily.

AGR (Adsorber for Gasoline Recirculation) is a new component from Pierburg... The intake manifold is covered with approximately 2mm of oil residue.
Unfortunately, I couldn't install it because the VW Fuzzi sent me the gasket for the exhaust manifold to engine block, not for the intake manifold.

Can anyone provide some information about the VCDS data?

Hello,

die Screenshots im 3. Upload sagen wenig aus, man sieht ja kein zeitliches Verhalten. Better logs.

The idle speed adjustment for cylinder 1, set at +2mg/H, also appears to indicate potential problems, but it's unclear whether this is a consequence of issues with the EGR system, a problem with the pressure differential (PD) element, or a problem with the cylinder itself.

I would check if the element is securely seated in the ZK (junction box), if the adjustment screw is tight, and if the connectors/cables from the PD (power distribution) wiring harness are in good condition.

Regarding the AGR (Abgasrückführung - Exhaust Gas Recirculation): I've attached a picture. Even though the engine is running at full throttle and a boost pressure of 0.35 to 0.5 bar is being generated, the measured air mass is too low. Later, it eventually rises to the expected values. To me, it looks like the AGR valve is sticking (or the solenoid valve that controls it), which would explain the poor regulation of the desired air mass during AGR operation.

Best regards, Rainer.

Hello Rainer,

I'll take the valve cover off again this weekend and check the positive electrode displacement (PED) of cylinder 1. Is cylinder 1 the one closest to the radiator?

The AGR (Abgasrückführung) valve was replaced along with the turbocharger (Pierburg). The old one was quite clogged and was leaking air from the ventilation holes for the diaphragm at the top.

I could completely seal the AGR (Abgasrückführung - exhaust gas recirculation system) and then perform a new measurement.

Could the problem also be caused by the upstream valve for the EGR system?

Best regards, Sebastian.

I need to ask some more questions now.

The boost control valve is number 19. As far as I can recall, a hose runs from it to the turbocharger, and another hose runs to the bypass/throttle valve (I hope I'm using the correct terminology).

Is valve 12 the control for the EGR valve?

"Is part number 15 even installed, or did I just miss it?"

Okay, I just took a quick look under the hood, and it's located behind the oil filter.

Is this valve, with the part number 1J0906627, the same as the one with part number 1J0906627A, and is it suitable for the turbocharger?

I also have an old DA1J0906627A turbocharger here that I could use for testing.

Hi,

The image is confusing to me regarding the routing of the hoses.
However, it can be quite easily traced along the hoses in reality.

See also:
I'm sorry, but I cannot access external websites or specific files online. Therefore, I am unable to translate the text from the provided URL.

Best regards, Rainer.

Hello,

I replaced the EGR control valve today, and I'm logging the data now, but I don't feel like it made any difference.

The PDE (presumably a person or department) checked the bolts, and they felt quite loose. The specified torque is 10 Nm plus an additional 120 degrees of rotation, and all of them were slightly tightened.

Camshaft - Exhaust lobe wear is present, but not severe enough to damage the lifters.

From the perspective of looking at the heat sink, the first PDE has a different boundary condition than the one at the end.

Also, the production date was approximately one year later than the rest of the vehicles, and it occurred after the car had already been delivered.

Attached is an empty log file with various parameters. Can anyone see anything useful in it?

Idle speed after about 1 minute, the EGR valve opens to 5% and the air mass increases. Is it normal for the EGR valve to close in this situation?

I inquired about PDE (fuel injection) units from Bosch in Bieberach, and according to their list, the part number 038130073BA should be used.

Installed on cylinders 2-4... 130073BA. Cylinder 1... 0130073BC. Will this fit?

Quote:

At idle, after approximately 1 minute, the EGR valve opens to 5% and the air mass increases. Is it normal for the EGR valve to close in this situation?

This behavior is normal.

The measured air mass at idle is approximately 480 mg/h, as mentioned previously.
Either your mass airflow sensor is measuring incorrectly, or the EGR valve is not closing properly, or you have another defect, such as excessive blow-by.

Best regards, Rainer.