ACV: Idle Speed Control Oscillates, Mass Air Flow Sensor?

Hello everyone,

My T4 / ACV likely has a problem with the mass airflow sensor, and I would like to hear your opinions on it.

Approximately 5,000 kilometers ago, the ESP (Electronic Stability Program) module on the high-voltage side started leaking. Of course, this happened right before the start of a vacation, so it needed to be fixed relatively quickly.

So, I got an AT pump from one of the usual online retailers and installed it.

"There have been previous issues with excessive black smoke coming from the exhaust when accelerating, especially when I suddenly press the accelerator pedal."
I had the ESD unit serviced and overhauled by a specialized company with original nozzles several times (less than 10,000 km ago).
ZMS hat ca 50tkm. Total mileage: 342,000 km.

The pump worked well for about 3,500 kilometers, the black smoke was somewhat better, but the "Aha! A new ESP, yay!" experience still didn't happen.
While you can't really call it a smooth idle, it does run and has power.

Then, suddenly, an error code appeared in the error memory, along with a glowing filament.

Error 17970 - Quantity setting (N146).
- P1562 -35 -10 - Upper limit value, intermittent.

The error typically occurs shortly (approximately 10 seconds) after the start, not when the ignition is turned on.
If the error occurs, it will happen consistently for a certain period of time.

Then he's gone again, even for hundreds of kilometers.
Then he'll be back...

He is not performing currently.

I checked something with VCDS and noticed the extremely fluctuating idle speed control.
In other vehicles, I've observed that the values tend to be quite stable and only fluctuate slowly and slightly.

In my ACV system, the readings fluctuate periodically around approximately 3 mg/stroke with a frequency of about 0.2 Hz.
The levels are slightly different. Some range from -1.8 to 1.1, while others range from -1.0 to 1.9.

(Scope attached, engine at operating temperature)

Intuitively, I would suspect a precision issue with the ESP (Electronic Stability Program).
Possibly a topic related to the feedback loop of the MSW (Municipal Solid Waste system), the MSW itself, or the distribution manifold.


Perhaps the errors are not related to each other?

There's a suspicion that the T4 has a chip tuning modification (via OBD), but I'm not entirely sure.

And why am I writing all of this?

1.) I'm quite fixated on the suspicion that it might be related to the ESP (Electronic Stability Program). Do you see it the same way, or am I being too narrow-minded?

2.) I still have a warranty on the ESP. But is it reasonable to expect the service provider to be able to fix the pump?
A reliable vehicle is very important to me. I don't drive it very often, but when I do, it's usually for long distances with a full load of passengers.

Thank you for your feedback.

Hello,

What is the fuel injection amount at idle, with the engine warm and no accessories like air conditioning or rear window heating running?
The fuel injection pump might be adjusted too "rich," which can cause regulation problems and also trigger the error message mentioned.

See:
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.

Auch den Riementrieb und beide Zahnriemen prüfen, nicht, dass sich hier etwas aufschaukelt.

Best regards, Rainer.

Good morning.

I have recorded another log. The engine was slightly warm (60°).

The amount of fuel injected is (unsurprisingly) not constant at idle, but varies by approximately 5mg per injection.
The log contains the value 2x (is it actual or setpoint?), as well as the control voltage and the setpoint voltage.

Everything is buzzing and humming along in idle mode...

Shouldn't they fit perfectly together?

After about 20 seconds, I slowly pressed the accelerator (while the car was stationary) and then experimented with the pedal.
According to the data, the results are much better at higher speeds, even though the engine achieves similar performance with a smaller amount.
It feels like the engine is running very roughly.

Therefore, I've included another log that shows the cylinder correction values when the idle speed is increased. However, it's unfortunately difficult to read.
Suggestion for KDataScope: It would be great if you could hide individual channels.

The ESP belt timing is okay, although slightly late. However, it's not perfectly consistent either.
The timing of the primary timing belt is also correct; I checked it when I installed the pump.
The tension of the ESP belt is okay; the markings are aligned.
I haven't checked the tension of the primary belt yet because I haven't been able to locate the indicator.

Best regards,
Frank.

PS: This post probably would have been better suited for the "Diesel Engine Technology" forum, but I can't change it anymore.

Hello,

Please check if all the belts are properly tensioned, and if the tensioners and pulleys are in good condition.
Also, make sure the ESP is securely attached to all (!) screws.

6mg/H is actually not a reason for misfiring, which means the cause is not due to an excessively high actual injection amount.

Best regards, Rainer.

Hello Rainer,

Everything looks fine.
The front screws of the ESP can only be visually inspected and checked by tapping them. However, they appear very solid and feel that way too.
The support for the ESD (Electrostatic Discharge) cables is securely fixed.

The belt tension looks good, and the pulleys appear to be in good condition.

I suppose I'll have to expand the ESP.

Okay, I guess I'll expand the ESP after all. Whatever.
I will let you know the result once I have them back.
Thank you for the tips!

Best regards, Frank.

Before you remove the ESP, check to make sure that all of its mounting screws have been used and are tight.

Is the central screw of the KW unit tight?
Have you ever looked at the values of the throttle position sensor?
hg
Herbert.

I agree with @Herbert; the "killer screw" was also a problem at ACV & Co.

And here is the final report.

It was the ESP.

All the screws were tight, including the central screw and those on the ESP itself.

I then returned the pump to the supplier. They disassembled it and informed me that:

... Significant contamination was found inside the pump and control unit. We cleaned the pump and re-calibrated it on the test bench.

I reinstalled the pump, of course, making sure the belt tension and dynamic timing were correct again.

Now the T4 is running as it should. There are no error messages, and the idle speed control is working perfectly. No cylinder has a fuel consumption exceeding +/- 0.5mg per stroke.

It doesn't produce nearly as much smoke as it used to, and it also runs more smoothly.

During the installation, I installed a new filter this time, and I cut the old one up on the workbench a little while ago.
Of course, there was some dirt in it, but nothing the filter couldn't handle. On the "clean" side, there wasn't a single crumb to be found.

I might upload another picture later, but my camera is acting up right now.

Here's the translation:

"As a final step, I'm including a log showing how the setpoint and feedback values of the mass flow controller should behave. This is for comparison in case someone else encounters the same problem."

Greetings and thank you.
Frank.

Thank you for the feedback!