limp mode no power help

W

widget2k13

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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?
 
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Erlingtheelder said:
The 'tell tale' sign all is not OK with this sensor is if the water temp gauge no longer goes to 90 C when the thermostat opens and stays there, or the needle behaves erratically. I believe there's possibly a logic loop somewhere in the system that compares the two signals and if they don't match may switch the engine control to 'limp' mode. Erling (the real 'elder). #5N007503
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I'm not sure that's true Erling, because there was someone recently complaining that their calculated fuel consumption was too high. This was because the second sensor is used by the instruments and calculates fuel consumption; in his case the second sensor was under-reading. In your case, perhaps the first sensor failed completely, which caused limp mode?

PS You should encourage your son to get his own account. I was beginning to think that you were younger than your son!

RAB
 
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another update :(
egr valve renewed (what a nightmare) ,all pipes removed and checked, test run still the same,
temp sender changed still reading 60 on temp gauge still the same.
thermostat changed temp now sitting at 90 whoop, limp mode still the same :(
 
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weird thing is i can drive around for hours locally as fast or as slow as i want and it never goes into limp mode, go for a 10 mile run down a dual carriageway at 70mph then slow down for a roundabout and try pulling away it goes into limp mode every time ?
 
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widget2k13 said:
Had every pipe off and checked and checked can't find anything
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Look again! You have a leak somewhere. Have you tested the N75? When you pressurise the lines, do they maintain pressure? Blank off one end, pressurise and then test with soapy water.

Given their age, I would replace the small rubber hoses. It won't cost that much.

RAB
 
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RAB said:
Look again! You have a leak somewhere. Have you tested the N75? When you pressurise the lines, do they maintain pressure? Blank off one end, pressurise and then test with soapy water.

Given their age, I would replace the small rubber hoses. It won't cost that much.

RAB
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Mine doesn't have the n75 valve fitted mine has a box in the drivers side inner wing
 
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widget2k13 said:
Mine doesn't have the n75 valve fitted mine has a box in the drivers side inner wing
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Start with replacing the vacuum lines. N02035327 is the part you need (5m). If that doesn't solve the problem, it lies within the box, possibly an internal leak. Can the box be opened? There is one on my son's Polo. I'll have a look later.

RAB
 
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RAB said:
Start with replacing the vacuum lines. N02035327 is the part you need (5m). If that doesn't solve the problem, it lies within the box, possibly an internal leak. Can the box be opened? There is one on my son's Polo. I'll have a look later.

RAB
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I've never had the box off itself the pipes all just come off by a clip
 
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widget2k13 said:
No only took pipe off one by one and blew down them with other end blanked off
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A vacuum leak may not show up with a pressure test. Best do a vacuum test.
Get a length of plastic tube tack it to a board to form a tall "U" then add enough water to form a seal either side of the U (like the drain under the sink). Connect one end to the vac system, then suck on the other, until the water level drops on car side, and rises on your end. Clamp the tube end you're sucking. If water differential is stable, no leak.
Mac.
 
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It's the ends of the tubes that might be the problem. If they are easily pulled off their connections, they might be too loose a fit. If length allows, cut the ends off and refit as a short term measure. Then replace.

RAB
 
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RAB said:
It's the ends of the tubes that might be the problem. If they are easily pulled off their connections, they might be too loose a fit. If length allows, cut the ends off and refit as a short term measure. Then replace.

RAB
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Hi Rab,
I agree with you on this, the pipe work perishes below the braiding allowing minute cracks that allow air to pass through under vacuum totally invisible because of the braiding, a hand vacuum pump is the way to test safely .
I bought a 5m length from TPS & replaced the whole lot as it will all be in the same condition
(15-20 years old).
Regards
Keith.
 
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Just had a look at my son's Polo. The tubes require a strong pull to remove. So if your's are easy to pull off, suspect the ends.

It looks as if the box lid can be prised off, but concentrate on the tubes for now. It's unlikely that the valves themselves are faulty, otherwise limp mode would be more easily triggered.

RAB
 
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RAB said:
Just had a look at my son's Polo. The tubes require a strong pull to remove. So if your's are easy to pull off, suspect the ends.

It looks as if the box lid can be prised off, but concentrate on the tubes for now. It's unlikely that the valves themselves are faulty, otherwise limp mode would be more easily triggered.

RAB
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I never removed the pipes from that end only from the ends where they led to and I blocked them at that end
 
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