limp mode no power help

hi, after years of trouble free motoring in my little a2 it has now decided to go into limp mode now and then, normally after the car has been running and done a few mile it loses all power.
turning the ignition off and on resets it and it works a little bit then goes again so i presume its in limp mode.
vag com shows code 17964, i have researched and found loads of different solutions, i have checked all the air pipes i can see and seem fine visually, the egr valve looks quite oily, there was a little oil around the pipe that goes into the throttle body and held in with a big clip.
i was reading about the n75 valve but mine doesn't seem to have one on the nearside near the header bottle ?
ive ordered a new fuel filter to start with the cheapest option.
any ideas what it could be or just go through everything i can find on the forums?
 

Jayw13702

Member
I’m guessing yours is a TD model.

That code generally implies low boost, I would be looking at the smaller vacuum hoses as well as the larger inlet hoses.

Look for splits and cracks and also listen for any hissing noises (difficult when you have a diesel clacking away)


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Menno

A2OC Donor
If you remove the skid plate under the car you might be able to see it, if it's split ofcourse.

Aft/bottom of intercooler split;
 

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hydo14

Member
Another thing that is worth checking is that the hoses running from the N75 valve to the turbo which are hose 24, 33 and 35 in the picture in this post are all actually good, on my car a visual inspection made me think that they were all fine however the rubber was actually completely disintegrated and the hoses were leaking. There's three of these hoses each running to different parts of the intake system and they are a thin bore plastic hose with a rubber end on them to connect to either the N75 or the turbo / charge hose.

The turbo ends of these hoses are all above the drivers side inner CV joint and then the N75 valve is mounted below the scuttle plate on a rubber mount in the space between the EGR and the passenger strut top mount. The picture below is what all of the rubber hoses were like on my car. I replaced these rubber ends with generic braided pressure hose with a 3.5 mm inner diameter however I am sure that TPS/your local audi parts dept / @CreweAudi would be able to help with getting the correct part. Also make sure to keep a track of where each pipe goes, I just replaced one at a time so I couldn't get it wrong, you'll notice that there's two black hoses and one green one.

Other forum members have reported that these hoses can wiggle themselves loose so could also be worth putting some small hose clips on them to keep them in place (My understanding is that these are actually pressure hoses rather than vacuum)

IMG_20210207_102332 (Large).jpg



I also had a large amount of oil around my EGR however on my TDI this was a red herring at least for this issue......
 
Another thing that is worth checking is that the hoses running from the N75 valve to the turbo which are hose 24, 33 and 35 in the picture in this post are all actually good, on my car a visual inspection made me think that they were all fine however the rubber was actually completely disintegrated and the hoses were leaking. There's three of these hoses each running to different parts of the intake system and they are a thin bore plastic hose with a rubber end on them to connect to either the N75 or the turbo / charge hose.

The turbo ends of these hoses are all above the drivers side inner CV joint and then the N75 valve is mounted below the scuttle plate on a rubber mount in the space between the EGR and the passenger strut top mount. The picture below is what all of the rubber hoses were like on my car. I replaced these rubber ends with generic braided pressure hose with a 3.5 mm inner diameter however I am sure that TPS/your local audi parts dept / @CreweAudi would be able to help with getting the correct part. Also make sure to keep a track of where each pipe goes, I just replaced one at a time so I couldn't get it wrong, you'll notice that there's two black hoses and one green one.

Other forum members have reported that these hoses can wiggle themselves loose so could also be worth putting some small hose clips on them to keep them in place (My understanding is that these are actually pressure hoses rather than vacuum)

View attachment 78317


I also had a large amount of oil around my EGR however on my TDI this was a red herring at least for this issue......
Thank you , but as mentioned In the post I don't see to have this n75 valve on my car ? I don't know why but there is nothing there lol
 

hydo14

Member
Thank you , but as mentioned In the post I don't see to have this n75 valve on my car ? I don't know why but there is nothing there lol
What is the engine? TDI AMF or BHC? From the service manual both of these engines should have the N75 valve. Maybe it has dropped down or something?

I don't have a picture of my TDI engine but I have marked the location of the N75 in red on a picture of an FSI engine bay and it looks like a small box with loads of hoses coming out of it per the picture above
IMG_20210102_124901 (Large).jpg
 

AndyP

Member
In my previous life with a 3 litre twin turbo engine renowned for complexity and boost leaks one of the things we did was presurise the whole intercooler system by fitting an adapter plate with a schrader valve in place of the air filter and connecting a compressor. This is very effective for finding leaks without the engine running.
 

kp 115

Member
hi, after years of trouble free motoring in my little a2 it has now decided to go into limp mode now and then, normally after the car has been running and done a few mile it loses all power.
turning the ignition off and on resets it and it works a little bit then goes again so i presume its in limp mode.
vag com shows code 17964, i have researched and found loads of different solutions, i have checked all the air pipes i can see and seem fine visually, the egr valve looks quite oily, there was a little oil around the pipe that goes into the throttle body and held in with a big clip.
i was reading about the n75 valve but mine doesn't seem to have one on the nearside near the header bottle ?
ive ordered a new fuel filter to start with the cheapest option.
any ideas what it could be or just go through everything i can find on the forums?
Hi widget2k13,
If your code does refer to low boost the line going to the turbo is a positive pressure & this controls a waste gate valve built into the exhaust manifold ( AMF) , this releases high pressure when you back off at high speed .
Mine at 197,000 miles was virtually seized when my cambelt stripped 32 teeth strangely just as i slowed from 60-40 mph.
The pivot arm has a bush that needed to be cleaned & then relubricated whilst the flat valve faces were cleaned & lapped in to give an air tight seal.

Hth
Keith.
 
As you can see I have no n75 valve , there is a little oil around the pipe going to the throttle body and looks like oil coming out the edge valve
 

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LordTJC

Member
You will have an N75 valve. Looking into the engine bay it’s in the top right under the scuttle area. It’s not immediately obvious. I had the same symptoms and code. When I went to replace my N75 valve I noticed one of the small pipes was disconnected. Connected it and all fine since. I suspect it got knocked off while doing work at some point.
 

hydo14

Member
As you can see I have no n75 valve , there is a little oil around the pipe going to the throttle body and looks like oil coming out the edge valve
Yes I am inclined to agree that the N75 is not where we have all described on your car. On my car it would be clearly visible from that angle that
your first picture is taken from. Can you try tracing the two hoses that come off your turbo charger. These should be visible from under the car looking up at in the area above the drivers side inner CV.

Excuse the badly repaired CV boot that the previous owner of my car left me as a present that now means that my turbo inlet side is coated in molybdenum grease.

IMG_20210206_142956 (Large).jpg
 

audifan

A2OC Donor
Looks like a BHC or ATL so N75 is not on the scuttle. It is located in a box. Try to find picture later. I still think it is the intercooler split though.
 
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