Exhaust restriction, 66kW ALH engine

Hello experts!

My A3 has been experiencing a strange lack of power in the lower RPM range for several weeks, between 1500 and 2500 RPM. However, it sometimes drives normally like before, and then suddenly accelerates powerfully when I press the gas pedal.

A noticeable issue is a brief hesitation or stumble when suddenly accelerating from the lower RPM range. This can be repeated indefinitely! In other words, there's a short jerk with every acceleration.

Maximum speed is reached. However, the fuel consumption is now about 0.8 liters per 100 km higher than before. I somehow have the impression that the turbocharger kicks in too late. Is that possible?

Hi.

The occasional power fluctuations remind me of a problem I had before.

I'm not sure if the 1997 ALH still has the small VTG membrane canister...

Regarding the issue with the intake manifold, I recommend starting by reading the error codes.

Okay, here's the translation:

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Hello Ulf!

Yesterday, I checked the issue with the stuck VTG (vehicle train operation). However, I couldn't find any clamps or obstructions. Using the 'suction on the jaws' method, the VTG could be easily and quickly adjusted to any position.

Another question... To check the airtightness of the vacuum hose system, do I have to disassemble each individual hose and test it for leaks, or is it sufficient to disconnect the supply line from the vacuum reservoir and 'suck' on it there?

Unfortunately, I don't have any information about the error memory yet!

Kickboxer wrote:

Do I need to disassemble each individual vacuum hose and check its tightness, or is it sufficient to disconnect the supply line from the vacuum reservoir and "suck" at that point to check for leaks?

Hi.

A single vacuum test will never capture all possible operating conditions --> solenoid valve open/closed.

As a temporary solution, I would try the following:
Den Unterdruckschlauch dort abziehen wo er sich mit dem Schlauch zum BKV vereinigt und daran saugen (also incl. (AGR).
It shouldn't be possible to constantly draw in more air.

Then, while the vacuum is running, apply battery voltage to both solenoid valves one after another. During the suction process, the VTG should be able to move, and air should not be constantly being drawn in again.

Okay, please provide the German text you would like me to translate into English. I will only provide the translation.
Disconnect the connector from the VTG solenoid valve and apply battery voltage to it.
The ventilation system must immediately switch to the other mode – and can do so repeatedly as long as the vacuum pressure supply lasts (with the engine idling).

If both tests don't show any error messages, try swapping the magnetic valves for the EGR and VTG systems.
While the EGR valve has a smaller cross-section for the vacuum path, meaning the variable turbine geometry (VTG) will likely build boost pressure more slowly, a functioning EGR valve is generally better than a broken VTG valve.

Hello Ulf!

I tested the VTG solenoid valve by applying battery voltage. It moves quickly and smoothly to the maximum position and returns to its original position when the voltage is disconnected. This can be repeated about twice, but then the vacuum pressure is no longer sufficient to fully move it to the maximum position.

'Is it possible to test the function of the EGR solenoid valve in a similar way? Wouldn't you be able to hear the clicking of the valve when you remove the voltage – meaning that the EGR valve would close?'

I have already tried this, but without the expected result. Disabling the EGR valve also did not improve the lack of power.

I still need to test the vacuum test you described and will post the results here later.

Kickboxer wrote:

I tested the VTG solenoid valve by applying battery voltage. It moves quickly and smoothly to the maximum position and returns to its original position when the voltage is disconnected. This can be repeated about twice, but then the vacuum pressure is no longer sufficient to fully move it to the maximum position. Question: Can the function of the EGR solenoid valve be checked in a similar way? Wouldn't you hear the clicking of the valve when you remove the voltage – meaning that the EGR valve would close?

Hi.

The EGR valve may not be testable in this way because the vacuum supply only feeds the variable geometry turbocharger (VTG).
So, in order to test the AGR magnetic valve, you must first replace the valves .

Hi Ulf!

As promised, I'm just posting the result of my 'hose inspection.' I replaced the hose that connects to the vacuum reservoir, as well as some other short hose sections that seemed suspicious between the solenoid valves.

What can I say, the engine is running again as it should. The power delivery is back to what it should be for a TDI. Small cause, big effect.

The only thing that's still present is the brief jolt when I suddenly press the accelerator. I guess, as you suggested, I'll have to get the error codes read.

Thanks again for your help with troubleshooting!