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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 February 26th, 2018, 06:30   #16
Windex
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Stupid question - have you checked the little (3") boost hose inside the ECU?

They develop a tiny little hole (very common) and can cause exactly your symptom.

http://forums.tdiclub.com/showthread.php?t=337801
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Old February 27th, 2018, 12:19   #17
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I have not checked that hose yet. From what I gather it's up under the windshield cowl? That's probably the vac hose that runs from the intake tube?
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Old February 27th, 2018, 12:30   #18
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Originally Posted by 2006PSDSD View Post
I have not checked that hose yet. From what I gather it's up under the windshield cowl? That's probably the vac hose that runs from the intake tube?
You will want to make sure that all of the vacuum/pressure hoses are intact, but no, the one that commonly develops a hole is inside the ECU. you need to remove the ecu from underneath the passenger side of the cowl and take the ECU cover off (4 screws) to get at the hose inside. there are two small clamps holding it in place. The original is black - this one has been replaced in blue - See here:

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Old February 27th, 2018, 16:41   #19
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If you've been driving the car all this time (281K miles) you may not realize the power has been dropping due to the vacuum lines, N75 valve and MAP sensor wearing out.

2006PSDSD should follow Mongler98's advice. It's through and not so hard or costly to do. You've gotten your money out of the old hoses, N75 valve and MAP sensor if they haven't been replaced. A local parts store wanted to sell me a new turbo for $600+ with no guarantee of fixing my problem, a problem that was not caused by the turbo or actuator. I replaced the N75 valve, hoses and MAP sensor. I now have a car that runs like new.
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Old February 28th, 2018, 08:23   #20
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My brother owned the car before me and he replaced all of the vacuum lines including the ECU hose with silicone hose from idparts at around 150k or so. He also replaced the n75 valve. Are the N75 valves very common to replace numerous times? Are the hoses also? I'm working on the list that Mongler gave me, but the internet side tracks my brain at times with things. I have all day Friday to inspect it all and I hope to find a fix this weekend
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Old February 28th, 2018, 15:33   #21
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I've never replaced one in 350k. Hosed it out once a while back.

If he replaced it with a cheapo valve it might need replacing again.

Silicone hose should be good for a long time.
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Old March 1st, 2018, 00:11   #22
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They last every 2-3 years for me at the most, no matter where they come from.

The silicone is good for a long time, I replaced mine after about 10 years.
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Old March 1st, 2018, 04:33   #23
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Good to know. The ones I have removed for other work are the silicone hose, so that's good. I guess there could always be a mouse that's hungry and chewed a hole in one though
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Old March 2nd, 2018, 11:59   #24
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When I check the n75 for the clicking sound, do I need to use a stethoscope to hear it, or is it pretty obvious? I don't hear anythi bff from it at idle, not can I feel is clicking
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Old March 2nd, 2018, 21:41   #25
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When I check the n75 for the clicking sound, do I need to use a stethoscope to hear it, or is it pretty obvious? I don't hear anythi bff from it at idle, not can I feel is clicking
I've had some that I can hear with the hood open, but also I've had to use a stethoscope on some too. Also have been able to just touch it and be able to feel it clicking.

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Old March 3rd, 2018, 06:38   #26
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Steve, does it just sit there and click at idle? Mine does absolutely nothing
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Old March 3rd, 2018, 07:58   #27
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I'm thinking N75 doesn't cycle at idle since there's no reason to be moving the TC vanes oops, I mean W/G.

N18 does sometimes.

VCDS can cycle it.
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Old March 3rd, 2018, 08:04   #28
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How much gunk is in your N75 valve and wastegate control line? I think it was Oilhammer that told me I'm likely just getting blowby past the rings~(these tend to wear by ~200k on the 1Z/AHU, along with 3rd cylinder scoring) finds it's way into the N75 and wastegate actuator hose and when enough accumulates, it gets clogged. The problem is worse when it's cold, because the gunk gets more viscous. At 15F it's probably solid. Problem is fixed by cleaning N75 and line (I use electronic parts cleaner) then blow it out with low pressure air. And then exercise and lube the wastegate because it's probably getting sticky from not moving as much.
Good news is it's cheap and easy to see if this is the problem. Bad news-if this is the issue-it will return once the gunk gets back in there and temps drop.
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Old March 3rd, 2018, 21:40   #29
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Steve, does it just sit there and click at idle? Mine does absolutely nothing
Mine seems to always be clicking away, even at idle. This would be both cars, the 97 Mk3 and the AHU powered B3V wagon. They both behave the same.

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Old March 4th, 2018, 06:26   #30
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Thanks again! I'm going to take a look at that line today. While I messed with things friday, I pulled the line from the n75 and blew some air through it to see the wg open. I swear the car had just a little better power in my travels up and down the mountain for errands. I'll have to grab some electronics cleaner today after church. This is the first I've read about any kind of cylinder issues in this car. I was blaming the oil on the ccv which I plan to reroute to keep thing cleaner

My n75 makes no noise at idle, Steve. I wish I had the vcds to cycle it, but I'm not spending that kind of coin.
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