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Discussion Starter #1
Like many others, I am chasing the culprit of the p0299 code on a 2005 BEW Jetta TDI.
I have replaced the N75, the VW shop has replaced the boost pressure sensor and test
drove with no codes. I have replaced the turbo hose with the dog collar and a few
vacuum lines.

I was content for a couple days of normal driving on flat roads at varying speeds. But
when I take it on the highway and proceed up long hills the limp mode is initiated and CEL
comes on after next time I turn the car on.

I read if removal of mass air flow sensor improved driving, this would be the problem.
The computer senses a missing MAF and uses a medium value to run with. I drove around
for 4 days with it disconnected and never had an issue besides a slight reduction in power.
Sweet!

So I replaced the mass airflow sensor and drove around all week. Everything ran great until
the uphill highway monster struck going to the mountains. Again I pulled the MAF, clear the
p0299 code and she ran good.

I guess its back under :dunno with a can of wd40 or starting fluid to see if I missed a vacuum leak but
thought I would ask.
 

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It's possible that there is a leak or blockage somewhere in the vacuum lines or the system coming from the VAC pump.

That is strange that the missing MAF only reduced power slightly. When I pull a good MAF I could feel a big drop in power. Are you sure that it's not in permanent low power so you don't feel the power drop?
 

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Discussion Starter #3
Since I have owned the TDI I would say she has 3 modes.
1- Runs great , sometimes too smooth
2- Limp mode, CEL reads p0299 slow acceleration and seems governed, very sluggish MPG 35-ish
2a- I can clear the code on the fly thru ODB2 with vag-com lite which until next uphill or increaesed demand puts me back into condition 1.
3- Pulled MAF reads CEL MAF faulty or missing , runs less than normal but better, MPG 40-ish last trip to mtns.
3a- Sometimes going up long incline with cruise you will hear a rev where it would call for downshift then level out. If I bump it to tiptronic mode this goes away.

* Both 2&3 usually accompanied by louder turbo hiss
 
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