VTG Issues: Emergency Mode, Intake Manifold Pressure Regulation Difference, etc. (Articles)

Fluctuating acceleration or intermittent acceleration, such as SDI instead of TDI; the magnetic valve for turbocharger pressure regulation and the vacuum hoses are definitely okay, but the turbocharger pressure regulation still doesn't work properly...

First, a visual inspection of the VTG (Variable Turbine Geometry) function should be performed: Immediately after starting the engine (by an assistant), if the VTG is functioning correctly, the threaded rod will be pulled approximately 1 cm towards the membrane chamber at idle speed and will remain in that position.
During short gas bursts, the rod moves back and forth by a few millimeters.

If the mechanism behaves differently, try disconnecting the hose from the charging chamber and using a large syringe (minimum 50 ml) to draw air from the chamber.
The threaded rod should normally be able to be gently moved to any position within the total stroke of approximately 1 cm using a syringe.
However, if the visual inspection during engine start does not show any movement or shows only very small movements, the VTG (Variable Turbine Geometry) often gets stuck in the idle or maximum position during the injection test, and/or it jumps to a position somewhere in between.

Common causes include excessive soot buildup in the VTG (Variable Geometry Turbocharger). However, in frequent, short-distance driving with minimal engine load, and consequently, limited lubrication by soot, condensation from the exhaust gases can also accumulate in the VTG mechanism and lead to corrosion.

Sometimes, it can also be due to a defective membrane dosing unit.
To verify this, the device should be removed and operated solely using the doctor's syringe.
The maximum stroke of the threaded rod is approximately 1.5 cm, and the rod should also move smoothly when operated with a syringe.
In the case of a defective container, replacement is practically the only option. At this point, it may be advisable to switch to a larger battery pack (see below).

To free up a throttle valve that is stuck due to soot or corrosion, the VTG (variable turbine geometry) must be moved back and forth between its extreme positions while the engine is running, until it moves freely again.
Sure, here is the translation of the text from German to English:

"There are many ways to do this."

1. Unscrew the cap and manually operate the threaded rod at least 100 times. Reattach the cap and adjust the threaded rod to its original length (this is very tedious and should be done after a cold start to avoid burning your fingers on the loader).

2. Using VCDS, access the basic settings within the boost pressure control measurement block.
This causes the VTG (variable turbine geometry) to oscillate between its minimum and maximum settings. Unfortunately, this only works when the engine is idling or with very little throttle. If one attempts to force the VTG with more gas or during operation, the procedure will be aborted and normal operation will be resumed .

3. Disconnect the connector from the turbocharger solenoid valve and, using temporary wiring, activate the valve intermittently with the vehicle's battery voltage, then deactivate it. Check if the threaded rod has moved approximately 1 cm.

4. Similar to principle number 3, but connect the valve to the connector of a turn signal bulb and activate the hazard lights.

5. Build your own electronics that control the valve at a rate of approximately 1 Hz, and that can also be activated under load during operation, allowing the stronger exhaust flow to more effectively blow away particulate matter. It is only recommended if it can be monitored via a pressure gauge to ensure that the pressure does not rise too high (which is very complex).

Unfortunately, success often only lasts for a few days or weeks. Sometimes, pushing the accelerator to the max on the highway can help.

More information about the VTG adjustment, its inspection, and function can be found in the technical article VTG Adjustment on VAG TDI Engines.
In case of malfunctions, also consider the VTG vacuum control or the electrical control of the VTG.


The more permanent, but more expensive, solution:

Replace the small coolant reservoir (approximately 5.5 cm outer diameter) with a larger one, as is installed from the factory in newer TDIs.
The AFN series enclosure 433483-1 can be easily replaced with the larger enclosure (approx. 7.5 cm) No. 434855-3. In this case, the larger heat shield No. should also be used. R7026940001 is to be installed.

You can (or used to be able to) find these parts, for example, from Schlütter Turbochargers for approximately 120 euros -> www.turbolader.com.
Update:
Unfortunately, individual Garrett charger nozzles are no longer available.
Alternative options: salvage chargers from scrap vehicles, inquire with auto recyclers, etc.

Here's a recommendation for attaching the threaded rod to the other container:
The adjustment range of the VTG lever on the loader should be approximately 1 cm. Otherwise, adjust it until it moves freely (especially if the stops feel soft and doughy rather than hard).
2. Adjust the rod so that the VTG lever, without vacuum, can be pressed against the "minimum LD" stop with a light force (approximately 5 N).
3. If possible, check the required vacuum pressure to achieve the set points, for example, using a large syringe and a vacuum gauge: The minimum set point should be reached at approximately 50 to 100 mbar, and the maximum set point should be reached at approximately 600 mbar of vacuum pressure.
4. Fine-tuning: During test drives with LDA (if necessary, using VCDS data logs), adjust the system to achieve early pressure build-up without significant overshooting during the adjustment process. Test: Perform the test in 2nd or 3rd gear. Accelerate from idle speed to full throttle.