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2004 JETTA TDI Turbo Underboost

2004 Jetta TDI-I have a P0299 turbo underboost code. The turbo is boosting after I start it, but quits after about 6 to 10 miles. If I shut it off then start again, it will boost for a little while then stop boosting again. The MAP sensor has ben changed. Checked vacuum lines-all are ok. Any ideas.
 

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Discussion Starter #3
Thanks for the info. I had looked at the vcds cable yesterday. Hate to spend the $250, but it is either this or the dealer.
 

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Only you can prevent yourself from being stupid!

I was getting the P0299 underboost condition, I was resigning myself to the fact that a VNT cleaning was in my immediate future but perusing the forum I thought, lets see if the vacuum system is in good shape (after I replaced all the hoses).

Vacuum from the pump was a nice 30 inches, and the brakes were good so I suspected as much. Checking the vacuum at the intermediate connections.. good good good.. ok lets see why the turbo isn't working, connect up to that and barely got any vacuum. Ok, well perhaps because it's not revving. propped up the gauge so I could see it through the windshield and rev the engine a bit, barely any movement. Odd thinks I to myself... so where is the vacuum getting hung up? tried from the source to N75 and not getting much there either.

Can you guess what I did?

I had the stupid check valve reversed! After I reversed that I was getting RPM plausible readings from the actuator connection. Put everything back and closed the hood and off for a test drive.

My scangauge II was reporting much better MAP values this time, before it would only go as high as 20 which made me think the turbo was trying to work but not doing as good a job as it needed to. Now on a WOT I was getting up to 30psi and yes, being set back down in the seat.

For those that know my history on my "new" Jetta I went from having a 2/3 clogged intake to a pristine one and now with my properly functioning turbo I'm getting better performance and oomph than I did when I test drove it.

Bottom line. it's the silly little things that get you!
 

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:thumbsup Good to hear!

I had a picture of a vacuum diagram for an ALH and BEW engines that I've been meaning to put up. It's now done, thanks for reminding me.
 
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