T4: Weak 2.5 TDI Performance - Troubleshooting

Our 2.5 TDI 5-cylinder engine with 111 kW is no longer producing the power it used to, and it's consuming more fuel. The mass airflow sensor (MAF) is okay, and there are no error codes in the diagnostic memory. On the highway, it now barely reaches 180 km/h (rated at 182 km/h), whereas 200 km/h used to be no problem. The tires are new! I've sometimes heard about a wastegate valve (or frog valve) that can be defective and cause a loss of power. Does anyone know more about that? Also, when shifting at full throttle, the turbo takes a long time to build up pressure again. That wasn't the case before.
Our workshop is a bunch of complete idiots! They completely messed up the chassis, and "disassembled" the electrical system! - But VW is to blame for this. And the vibration damper on the crankshaft also fell off last week...

Hello!

It sounds like there might be a problem with the VTG (vehicle traction generator). Please check the troubleshooting and knowledge database for information on things like inspecting the VTG linkage, etc.

Greetings,

Peter.

Have you ever considered simple things like clogged diesel filters? When the engine is running, check for air bubbles in the fuel line between the diesel filter and the fuel injection pump (and try accelerating while doing so).

Best regards, Rainer.

Hi, the diesel filter was just replaced. Today I checked the VTG linkage and, sure enough, it was squeaking and hard to move. So I sprayed some WD-40 on it and took it for a test drive. It's working much better now and the engine revs willingly above 4000 RPM. Just one more question: I doubt the WD-40 will last long. What kind of lubricant can be used for the VTG? Would copper grease be suitable due to the heat? I would appreciate any suggestions. Thanks.

See VTG rods.