Low Air Pressure: Audi A4 Performance Issues (Up to 2500 RPM)

Hello,

'I've been experiencing a significant problem for quite some time. My A4 2.5 TDI with the AKN engine doesn't have enough power below 2500 RPM. This is especially noticeable in the higher gears. Above 2500 RPM, it suddenly picks up power, and reaching the top speed isn't an issue.'

I took the car to the workshop -> The mass airflow sensor (MAF) was replaced because the air values were too low -> No improvement!

I was back at the workshop -> Test with a new mass airflow sensor -> Still no improvement!
After that, they tested the vacuum system for leaks -> it was okay. The valves also seem to be working properly. Additionally, they checked the pressure sensor on the turbocharger to ensure it was functioning correctly.

They now suspect a faulty turbocharger (72,000 km). However, the strange thing is that it really kicks in from 2,500 RPM, but doesn't do anything before that. This always happens, so it's not sporadic.

What could that be? One thing is clear: the lower mass airflow (MAF) values also reduce the fuel injection volume. But why are the MAF values too low, and then suddenly everything is fine again above 2500 RPM? (Note: If you only accelerate gently, you hardly notice anything - it's only when you press the accelerator pedal more firmly).

Thank you in advance.


Best regards,
Jörg

Hello, fellow namesake.

How about trying the 'search' button? I think you'll find plenty of reading material and opportunities to discover errors there.

I would initially suspect a small leak in your charging air duct.

Yes, yes - of course, I did some research and found many things. And then I asked those who might be suitable about their approach to solving the problem.

Of the 3 (three!!) that were relevant to my problem, almost all responded with: '...is still broken,' '....I've replaced this and that and that, and it still doesn't work!' or the answer was simply: '...I've come to terms with it and will never drive a diesel again, let alone anything else from VW/Audi!'

While this has been confirmed again by the latest J.D. Power study, it doesn't help me. So, I used the SEARCH function.

And regarding your comment - The air tightness of the system was checked. If there were a leak, wouldn't the performance suddenly improve above 2,500 RPM?

Best regards,
Jörg

Yes!

Consider the following points:

I'm sorry, but I cannot provide a translation without the text you would like me to translate. Please provide the text from the URL you mentioned, and I will be happy to translate it for you.
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.

This also applies to the AKN.

Before you start complaining, how about providing the mileage, relevant measurement values, cleaning instructions, and a diagnostic report for the AGR valve?

Perhaps a stuck AGR valve is the cause... It could also be a small leak in the charge air system.

So:

72,000 km and regarding the measured values, I can only comment on those provided by the workshop. The MAF (Mass Air Flow) sensor readings are significantly below the expected values; they are only around 500 across the entire range. This results in too low boost pressure (values).

So, I'm assuming that the turbocharger isn't building any pressure, which means it's drawing in too little air. This would explain the low mass airflow readings.

But why does it suddenly accelerate and reach its top speed starting at 2,500 RPM?
Assuming the turbocharger is faulty, could this potentially cause symptoms like the ones described? (Maximum speed > 220 km/h)

I'm just trying to rule out possibilities, because the workshop suspects a faulty turbocharger, but frankly, they don't really know what's wrong.

Best regards,
Jörg

Let's take it slow and think logically, for once!

It seems the turbocharger isn't building enough boost, but it's present above 2500 RPM, so it's unlikely the turbocharger itself is completely broken, right? What else could it be? Perhaps a sticking or jammed variable geometry turbo (VGT), a faulty turbocharger pressure solenoid valve, or an issue with the control pneumatics. Please check the two links I sent and review everything mentioned there! Then we can proceed further.


And without measurement logs, we probably won't be able to proceed.

Hi,
It's all in the links. I suspect a stuck or incorrectly adjusted VTG (Variable Transmission Gear).

You'll have to measure and verify those things yourself.
If you don't want to or can't do it yourself, then all that's left is to go to the workshop with a full wallet.

A faulty VTG (Variable Turbine Geometry) seems likely, according to the workshop's assessment. Are there any ways to permanently fix it? And what's the easiest way to test the VTG?

Best regards,
Jörg

When are you finally going to start searching and reading?

Hello,

The problem I described earlier has been resolved. It was the boost pressure control valve.

My great Audi workshop was incredibly incompetent, taking 2 days to identify the problem.

'...we've checked everything - it's all okay.' And when I asked about the tax valves,

I also received a confirmation: '...yes, those are also fine - now it can only be the turbo.'

'to be...'



I'm increasingly understanding why German manufacturers consistently perform well in all tests and surveys.

...are once again on par with Italian quality. Especially VW is making progress.

making significant progress.


It was actually an independent workshop that had been a Honda dealer for 18 years that did it.

Problem solved.
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