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VW MKIII-A3/B4 TDIs This is a discussion about MKIII-A3/MkIII Jetta/Golf (<99.5) and B4 Passats (96,97) TDI's. Non TDI related postings will be moved or removed.

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Old September 7th, 2010, 05:44   #1
Sayray24
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Default N75 boost control solenoid

how easy/hard/expesive would it be to replace the boost control solenoid on my 1998 jetta? once i get above 2800-3000rpm at 1/2 to full throttle it starts pulsing/surging.
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Old September 7th, 2010, 09:44   #2
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Hmmm, sounds like the intake manifold may be clogging up, dirty MAF connector and some hole in one of the intercooler pipes(very small hole, thus higher pressure makes it bleed).

N75's do or don't work...
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Old September 7th, 2010, 09:52   #3
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Quote:
Originally Posted by bikeprof View Post
Hmmm, sounds like the intake manifold may be clogging up, dirty MAF connector and some hole in one of the intercooler pipes(very small hole, thus higher pressure makes it bleed).
N75's do or don't work...
When I had my RC2+ installed, my N75 was limiting the car to 10.5 lbs of boost. I didn't notice since that's almost stock. A few taps and some cleaning got it a little above that, but only when I swapped a new one on did I get the full 17 lbs requested.

I agree though, it sounds like a different problem is afoot.
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Old September 7th, 2010, 10:59   #4
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huh ok well i read a post that had the exact same symptoms and they said it was the n75 wearing out.
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Old September 8th, 2010, 05:14   #5
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Quote:
Originally Posted by Sayray24 View Post
how easy/hard/expesive would it be to replace the boost control solenoid on my 1998 jetta? once i get above 2800-3000rpm at 1/2 to full throttle it starts pulsing/surging.
I had the exact symptoms you have. After a lot of testing for pressure leaks and the turbo actuator it came down to the N75. Funny thing was the N75 tested good statically. I have no means to test it dynamically and that was the problem, it must operate at around 20 hz or so. Putting in a new N75 fixed the surging. I did not replace any vacuum hoses or anything else since they all tested fine. I did break the ECU MAP sensor nipple though.
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Old September 8th, 2010, 05:39   #6
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The diaphragm on old N75s gets stiff and cannot function properly. Replace it. ~$50 for a Pierburg generic one.

Do the vacuum lines from the N75 while you have it all apart.
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Old September 8th, 2010, 09:18   #7
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Paramedick-

What source for that $50 boost solenoid?
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Old September 8th, 2010, 09:26   #8
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http://shopping.boraparts.com/produc...roducts_id=378
http://www.idparts.com/catalog/produ...roducts_id=451
http://www.metalmanparts.com/product...&categoryId=-1
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Old September 8th, 2010, 10:15   #9
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thanks for the info guys. what would be the possible consequences of just letting it go for now? seeing as how i usualy shift before or right around 3000rpm
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Old September 11th, 2010, 09:52   #10
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Quote:
Originally Posted by paramedick View Post
The diaphragm on old N75s gets stiff and cannot function properly. Replace it. ~$50 for a Pierburg generic one.

Do the vacuum lines from the N75 while you have it all apart.

Could this be the very intermittant problem I have with my 2000? Once and a while it will fall on its face about 3000 rpm. You cannot get it to redline. It may do this 2 or 3 times, then everything will go back to normal and not do it again for 6 months.
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Old September 19th, 2010, 19:00   #11
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well the jetta is going to the shop this week so hopefully they will find the problem
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Old September 23rd, 2010, 16:31   #12
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well the mechanic acknowledged that there was something not right but he could not pinpoint the problem. he thinks it might have something to do with the axel wearing out or something like that.
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Old January 18th, 2011, 13:46   #13
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Quote:
Originally Posted by paramedick View Post
Do the vacuum lines from the N75 while you have it all apart.
What are the specs on these vacuum lines/place to buy them?
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