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Discussion Starter · #1 ·
Hey everyone. So I bought this 07 gti from someone with a broken timing belt. Replaced the head, timing belt and accessories, put it back together and took it for the first test drive. After driving normally for a bit, decided to get on it a little. Boost gauge spiked to 22lbs and car went into limp mode with 0 boost. Turned the car off and had boost again but the same thing eventually happened again.

Replaced the boost solenoid, no change.
Replaced the boost pressure sensor, no change. I don't know what else to do at this point. The turbo isn't making abnormal noises. Would a diverter valve cause this? I don't have vag com.
 

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Boost solenoid? You mean the N75-boost frequency control valve? You would still make boost but would fluctuate badly and not reach normal peak initially.
Boost Pressure sensor? You mean the MAP sensor? If failed it would not allow it to know if were overboosting, right?
A torn or failed piston in a DV can cause loss of boost but would not likely cause an overboost situation unless stuck shut due to failed solenoid. VCDS could allow you to do output tests.
The MAF can do this...see if it builds boost with the MAF disconnected. The PCV can as well...remove it and test its ability to seal at its check valve as well as its diaphragm. The rear breather tube should be open as well when forcing air into the top of it. Seems everyone has found varying solutions to this P0234 code.
 

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Discussion Starter · #3 ·
Right, i changed those two sensors because ross tech suggests they could cause the issue. Ironically they were both broken. The n75 hose barb was broken off and the little sensor inside the map was missing but they didn't fix the overboost. So I'll try what you said and update. Thanks for the advice.
 

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This is too often the case...so remember that. We often think a problem will be solved with just one bit replaced and often it is a compound state of failings. I always find this to be true and just work through all of the possibilities beginning with easiest and cheapest to sort first...and eventually you have covered all of it.

So, yeah, keep the post updated and eventually it'll get sorted and a solution will be left for future viewers.
 

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Discussion Starter · #6 ·
K so I got vagcom. Here is what it's telling me. While driving, the n75 stayed at 0% through the rpm range.
On ross tech, it said something about performing basic setting for the charge pressure control and an output test for the turbo. Anyone know what the group codes are for this?
(From Ross tech)

Possible Solutions
  • Check Charge Pressure Control System
    • Perform Output Test (to check the Turbo Charger)
    • Perform Basic Setting (to check the Charge Pressure Control)
    • Perform Pressure Test to locate Leaks
  • Check/Replace Boost Pressure Control Valve (N75)
  • Check/Replace Boost Pressure Sensor (G31)
  • Check/Replace Turbo Charge

Vagcom

000564 - Boost Pressure Regulation

P0234 - 001 - Limit Exceeded (Overboost Condition) - MIL ON

Freeze Frame:

Fault Status: 11100001

Fault Priority: 2

Fault Frequency: 1

Reset counter: 255

Mileage: 177409 km
Time Indication: 0

Date: 2000.00.00

Time: 19:06:50

Freeze Frame:

RPM: 5734 /min

Load: 100.0 %

Speed: 79.0 km/h

Temperature: 82.0°C
Temperature: 12.0°C
Absolute Pres.: 970.0 mbar
Voltage: 14.097 V
 

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Testing the wastegate requires removing it for inspection or pressure testing its operation.
Basic setting VCDS says MVB(measure value block) 011.
Output test are selective or sequential. The instructions are here;VCDS online manual; http://www.ross-tech.com/vcds/tour/out_test.php

If you unplug the N75 and test its ohms across the two prongs of the N75...it should be between 25-35 ohms. Outside of that range and the N75 should be replaced. This was information given to me and mine tested at 22 ohms. Replacing it was the fix of the symptoms mine was then having. But given you just replaced the N75...makes me think the hoses aren't connected correctly with regards to orientation onto the N75 or was done so loosely.

More likely it is a problem with the N75 and how it was installed because you are making boost but it is unable to regulate it by operating the WG or DV properly. I doubt the DV will cause this because it should be shut unless it isn't opening when throttle is released. Doubt it is the MAP because it is new. Are you positive the WG isn't stuck shut? Perhaps was damaged somehow or the previous owner did something with the linkage or its preload setting?
 

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Discussion Starter · #9 ·
Thanks for all of the info. So, put the car on the lift and there is oil all over the dv and turbo, oil in charge pipes as well. Not sure if this was a result of the overboost as it wasn't there before or if the turbo seals were shot and they finally blew out. Either way.. I didn't have any time to pull parts. It was actually in the air to test the wg (which is not seized). So this weekend's project is a new turbo, revised dv and a good cleaning of pipes and sensors to get rid of the oil. Also going to triple check all clamps and hoses to make sure everything is tight. I will report back soon!
 

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I know this is old but at 5min they show testing the WGA and WG function;
 
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