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Sorry for a repeat post, but figured I had posted in an incorrect area the first time, and did not know how to fix that.
This weekend, I drove from Yuma AZ, to Flagstaff AZ. On I-17, North of Phx, at around 6000 feet in elevation, I felt a sudden loss of power. I do have a boost gauge installed, so when I felt the sudden loss of power, I looked at the gauge and it was registering zero boost. I drove the remaining 30 miles into Flagstaff, having to downshift and not being able to maintain the 80 MPH speed that I had been maintaining with ease. It would manage 80 plus on flat ground, but there was not enough power to maintain that speed on any grade. However, upon turning the car off at the hotel to register, I noticed that I once again had boost when we drove down the street to get something to eat. I drove the car around for two days in Flagstaff, with no issues with the turbo again. That would include three trips up the mountain to the "Snowbowl" ski area, which is over 9000 feet above sea level. The turbo functioned flawlessly going up the hill there.
Upon heading back to the Phx area, once again I encountered the loss of the turbo. This time I had been cruising along in fifth gear, cruise control set at 80 with no problems maintaining the speed. I had to tap the brakes to slow a bit, because of a truck that had pulled into the passing lane to go around another slower moving truck. Upon trying to accelerate back to the cruise speed, I once again noticed the turbo kick out, and again I had no power. The boost gauge was reading zero again, and regardless of what was done, downshifting, etc.. it made no difference. Remembering that I had shut the car off, and upon restarting at the hotel I had boost, I decided to put the car in neutral, and shut off the ignition on a short downgrade. When I turn the ignition back to run, and let the clutch out in fifth gear, the car restarted and once again had the turbo back online. The turbo never dropped again on the following 270 miles home. I did however notice, at that time, a little higher boost readings that I am used to seeing. I assumed it was just the elevation, because all appeared to be normal again, once we dropped back to the lower elevations where I am used to driving.
Anyone have any ideas of what happened, or where to begin looking for trouble? The car is a 1999.5 Jetta with 130,000 miles. New injection pump, and timing belt at 126,500. Trouble free driving since that time, returning 49-50 MPG driving with the cruise set between 75-80 on my highway trips.
I will assume that all the vacuum hoses are the factory hoses, and are most likely overdue for replacement. Something that I will attack, but was wondering if anyone could tell me what diameter of hose I will be needing to purchase for that job? Are all the lines the same size? If so, approximate feet of hose needed to replace all? Any suggestions on hose type/brands that will be superior in performance as far as longevity goes?
 

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Yes, you have classic limp mode. Turning off the ignition reset the power. Basically, the computer is monitoring sensors and whatnot and when something important goes out of bounds, it cuts boost to prevent damage. 3.5-4mm hoses will do the trick. The OEM lines withstand oil better but silicone will stay softer and not fray and crack as easily.

FYI, don't be afraid to rev the engine, especially at high alt. Lugging the engine is never good but lugging at high alt can cause damage to turbo by stalling the turbines. See this article for more tips on limp mode troubleshooting; http://www.myturbodiesel.com/1000q/multi/limp-mode-TDI-fix.htm
 

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Wondering if you ever figured out that problem. I have a 2003 Jetta with that exact same problem, I may buy the software to scan the car, I have replaced the turbo,not the actuator, it worked fine when I pulled a vacuum, the N75 selenoid, and alot of vacuum lines.....It killing me.....
 
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