2006 Jetta TDI Issues: Calling experts, tinkerers, TDI-Masters, and Mechanical Minds

TDI'ers,
I am new to the forum, but I've been driving a 2006 Jetta TDI for some time now, and I need the help of anyone who's "got the knack."

I'm getting a "Lack of Boost Pressure" code, and the car's Turbo is struggling to go up hills at any normal speed. The turbo will spool up and work at times when the engine is cold, but once it warms up, it stops boosting and the check engine light will come on if I'm going up a hill.

Does anyone know what could be causing this?
My dad thinks it could be the turbo waste gate actuator, but any other clues or ideas? Anyone else have this issue?


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For those wishing to know more about the history of the car and problem, let me give some specs and maintenance real quick for the vehicle:
~189,000 miles
5-Speed Manual
1.9 TDI engine
Replaced Dual Mass Flywheel with Single Mass, New clutch as well.
New pressure plate and throw out bearing.
Replaced Timing Belt, Belt Tensioner, Water Pump while new clutch was done and engine out..
Replaced in line fuel filter cartridge
Replaced all (4) Rotors with High Performance Ventilated Disc/Rotors and new Ceramic Brake Pads.
All new Radial HP Tires, front end aligned at that time.
New K&N Lifetime Air Filter (Replaced in August).
Shift Linkage adjusted
New Motor mounts installed October 2015, full service.
Upgraded Motor Mount Kit. (Diesel Geek Brand)
4 Brand New Tires, installed April 2016
Replaced Slave Cylinder September 2016

I've driven this car across I-70 multiple times from Utah to North Carolina. In May of this year, a friend and I made our way to Arkansas for a job, and the car was doing great for the first couple hours. When we hit about Grand Junction, the Check Engine Light came on and the turbo sputtered. After the code was cleared, I nursed the car to Arkansas, and 3 weeks later to North Carolina. The code was cleared, and it was used all summer without issue.

I returned to Utah in late August, and the engine light came on again only hours into the drive. The turbo quit working, hills had to be driven over below 60 mph as the engine lost power, but I made it to Utah. Got it into the shop, they fixed the slave cylinder and said, "At this many miles, the turbo is just gonna fail soon." They cleared the code, I drove it for two weeks, and few issues arose. I drove a mountain road and again the check engine light came on, and all turbo was lost.

I completely took apart and cleaned the EGR, replaced the fuel filter again, replaced a couple of fuel lines and vacuum hoses, and a shop just reattached and tightened a hose to the turbo itself. All to no avail. After cleaning the EGR, I drove it immediately after and it seemed to be fixed. The turbo spooled, the power was there, I pulled hills at high speeds and things went well. The next morning though, again the check engine light came on and power was lost.

That's not high miles at this point.
You don't have a turbo "wastegate" actuator. The turbo is a variable rate boost that is controlled by the actuator. It could be faulty. Not sure if it's vacuum /electric controlled or completely electric operated.
Get rid of the K & N air filter. The stock one is vastly superior in keeping particles out of the engine intake/turbo and will flow more air than a stock TDI is capable of using.
A log reading of the MAF actual vs requested under load may determine if the MAF data is faulty. VCDS required and may give additional insight into your boost code. A log of boost (MAP) values also.

When the turbo actuator develops a hole in the diaphragm it may work sometimes and other times not. Temperature may play a role in how pliable the diaphragm material is and whether or not it can sustain it's vacuum holding capability when there is a tear.

A quick test with a MityVac hand held vacuum pump on the actuator nipple will tell you whether there is a leak in the diaphragm.
The Mity Vac should be able to progressively draw down and hold the position of the actuator rod with every pump of the handle.

The engine's vacuum pump can overcome the leak at times because it has a much greater ability to create a vacuum...especially at a higher engine RPM. The Mity Vac does not. You can't pump it fast enough to match the vacuum pump's capability. So, if there is a leak in the diaphragm the vacuum will drop quickly.
If it drops at all then you have the potential to lose control over the turbo.

It that all checks out then you have elsewhere to look like the vacuum hoses and vacuum source.

What are you reading codes with?