TDI Idle Issues: Pump Düse Problems & Fixes

Dear DIY enthusiasts,
I've posted about this issue before, but haven't found a solution. My Audi, a 2.0 TDI with engine code BRE, pump-injector system, and DPF, has 165,000 km on it. It starts perfectly, has power, and drives without any noticeable symptoms. The only problem is that the idle is unstable, as if the idle speed control isn't working correctly. I've tried various things so far, but nothing has worked.
The following measurement blocks (MBs) were measured on different days with the engine at operating temperature. All measurement blocks remain approximately constant, except for MB 13. Based on the data, cylinders 1 and 2 appear to be performing well, while cylinders 3 and 4 are weaker, but not consistently.

MWB 1 (followed by a blank line)
Speed: 882
Injection volume: 4.7 – 4.9.
Duration of boost (should be): 7.1 – 7.7
Coolant: 83.7

MWB 3
Speed: 882
AGR (Target): 255
AGR (is) 255.
EGR control: 58.6

MWB 4
Speed: 882
Start of funding (target): 0.
Funding duration (target): 7.1 - 7.7
Twist angle: -0.5

MWB 10
Air mass: 250-265.
Ambient pressure: 979.
Boost pressure: 989.
Accelerator pedal position: 0.0.

MWB 11
Speed: 882
Boost pressure (target): 1030.
Boost pressure: 989.
Ansteuer. Boost pressure: 78.9.

MWB 13 Cylinder 1 Cylinder 2 Cylinder 3 Cylinder 4
-0.33 -0.33 -0.00 0.71
-0.31 -1.48 0.47 1.34
-0.42 -0.80 -0.14 1.41
-1.27 -0.05 1.44 -0.09
-0.87 -1.18 0.78 1.27

MWB 18
Cylinder 1: 0
Cylinder 2: 0.
Cylinder 3: 0.
Cylinder 4: 0

MWB 23
Cylinder 1: -35
Cylinder 2: -14
Cylinder 3: -30.
Cylinder 4: -32

What could be the reason for this change? I would understand if a value was consistently better or worse, but I don't understand why this value is fluctuating like this. What could be the cause?
Does anyone have an explanation for this? I'm just stuck and can't figure it out.

Best regards, audifriend.

Hi,

If the "bad" cylinder is located in measurement block 13, I would investigate the belt drives and auxiliary components.

Best regards, Rainer.

Hello,
I once had a vehicle with similar symptoms: an unstable and somewhat "grumbling" idle. In that case, the freewheel mechanism of the alternator was defective. You can relatively easily narrow down the problem to either the engine or its auxiliary components by temporarily removing the serpentine belt as a test.

Best regards,

Thank you for the suggestions. I will investigate further and report back soon.

Best regards, audifriend.

In my daughter's A3, the dual-mass flywheel was the cause of the uneven engine idle.

Rüdi wrote:

In my daughter's A3, the dual-mass flywheel was the cause of the uneven engine running at idle.

Don't scare him. However, based on my experience, I can confirm that the clutch and dual-mass flywheel (DMF) are very robust in terms of torque with the BRE.
Indeed, there was a faulty batch of those.

I would still start by checking the auxiliary components.

@audifriend:
At your mileage, the oil pump drive might be starting to fail soon...
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.

Otherwise, the powertrain is great. My car with a manual transmission and rear-wheel drive was sold with around 340,000 km on it and ran perfectly without any oil consumption.

Thank you for the information. I plan to take a look at everything in person next week. As for the auxiliary components, only the generator, water pump, compressor, and hydraulic pump are relevant. I've already taken a look at the generator pulley; it doesn't seem to have a freewheel mechanism. I will also examine the timing belt drive, but I can't imagine finding anything there. However, I will see what happens.

Okay, so this weekend I took a closer look at the timing belt drive and auxiliary components.

Timing belt drive: Timing and tensioner are okay. The camshaft for the intake valves showed a very slight deviation when inserting the 6mm dowel.

Nebenaggregate: Zahnrippenriemen entfernt und Motor laufen lassen. Keine Veränderung. Generator hat tatsächlich eine Riemenscheibe mit Freilauf. F"reilauf" is okay.

Sometimes I think I'm too sensitive. But even my passengers say that the engine runs a little rough when idling.
By the way: There's no change when I press the clutch pedal.

Hello,

It's possible that the AGR rate is too high due to excessively high mass airflow sensor (MAF) values. If the MAF sensor measures too much air (e.g., due to a faulty aftermarket sensor or vacuum leak), the system attempts to compensate by reducing the amount of fresh air and increasing the intake of exhaust gases.
This can also lead to an unstable idle speed because excessively high mass airflow sensor (MAF) values don't necessarily mean that the actual amount of fresh air being drawn in is larger.

Best regards, Rainer.

Thank you for the information.
I've also considered that possibility because the exhaust smells unpleasant when the car is idling. Also, I had problems with the exhaust opacity during the last technical inspection; it was above the limit of 1.0 instead of being at or below 0.5. As a result, I inspected and cleaned the entire EGR system. I suspect that the EGR rate is too high at idle, but this isn't reflected in the measurements.

The mass airflow sensor (MAF) is still the original part. I had replaced it once with a new one from Pierburg, but then switched back to the original because of the reasons mentioned above, even though the Pierburg one felt slightly more responsive.

If I understand the logic in the MSG correctly, there is an EGR value stored in the MSG for each LMM (mass airflow) value. The EGR system can be controlled hydraulically or electrically. A rotating potentiometer provides feedback on the EGR value to the MSG. However, the actual EGR rate may be higher if, for example, the exhaust backpressure increases due to a clogged DPF (diesel particulate filter). The ratio of fresh air to recirculated exhaust gas is actually only correct in relatively new vehicles, as the equilibrium state between fresh air and exhaust gas changes with mileage. This is probably not taken into account by the MSG.
Once, my car displayed a message indicating that the DPF was full. In reality, the differential pressure sensor was faulty and had to be replaced. Later, due to the circumstances described above, I had the DPF cleaned. Allegedly, 45 grams of ash were removed. However, this had no effect on the rough idle. It was just a waste of money.

Hello,


The AGR (Abgasrückführung) is a control loop with a setpoint and actual value for the mass of fresh air being drawn in [mg/stroke].
The EGR valve is simply controlled to achieve the target air mass value.

The aging of the mass airflow sensor (MAF) can be counteracted by reduced intake air mass due to carbon buildup, etc., meaning that the exhaust gas recirculation (EGR) rate will remain approximately the same.

It might be worth checking if there's a software update available for your engine control unit (you can post an Autoscan or KOBD2Check will also show it).

Best regards, Rainer.

Hello,

Here's the log file I generated using Autoscan. How can I tell if the software for the engine control unit is the most up-to-date version? Should I go to a dealership and inquire there?

Hi.

Quote:

Part number SW: 03G 997 012 HW: 03G 906 016 GB. Part: R4 2.0L EDC G000SG 1348

There was definitely an update already.

Yes, the Audi dealer should know that. Your data set is 03G 997 012, software version 1348.

If you search for the software part number on the web and find a software version greater than 1348, then you do not have the current version.

In most cases, as long as you don't encounter any problems, this isn't a big deal. Because the new software might have fixed one bug but introduced a new bug or issue in its place.
Relying on software updates is only for suckers.

If you are experiencing a noticeable problem, it might be worth having the latest software version installed (flashed).

Best regards, Rainer.

Thank you for the interesting suggestions.

I did some research on this topic online. The problem with the unstable idle is not an isolated case. Apparently, the EGR rate is too high. The solution: Install a gasket with a smaller opening (part number 028 131 547 B) in the EGR recirculation system and update the software from version 1348 to 9886. Then, the engine should run smoothly again. Is this the solution?

Quite possible. X

You can try disconnecting the EGR valve connector as a test; this will prevent it from functioning. While this will put the car into a limp mode with reduced power, if the engine runs smoothly at idle in this state, you've likely found the cause of the problem.

The AGR valve is located right next to the throttle body.

Best regards, Rainer.