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Discussion Starter #1
i just bought a 1999 tdi jetta i got it at a great price because the check engine light is on and its running at low power.... limp mode i assumed. i figured it would be a simple fix so i bought it ..... i tinkered with it for 15 hours yesterday and i'm still having the same issue.

code comes up as p1550 pressure control difference.
when i start the car the light is off for around a minute to a minute and a half it drives with full (or what i'm assuming is full power all 90 hp worth) power and then the engine light comes on and it feels as if its not making any boost. (i can still barely hear the turbo tho.)

first thing i did was change all the vaccum lines.... nothing

then i cleaned the intake (it was horrible) still no change.

i swapped the n75 with the egr regulator (i was told i could do it for testing) this still made no difference

i went back to autozone and had the codes cleared . this time it ran for maybe five minutes before the check engine light went on. i went back up and had the codes re scanned and had the same code p1550

next i unplugged the maf this didnt make too much of a difference. some but not much.

the wastegate actuator is working i hooked it directly to the line (bypassing the n75) while at idle and it sucked the rod down around 1/2 a inch maybe a bit more couldnt see too well just feel.



now i'm frusturated and stumped because i figured itd be a easy fix. it might still be i just cant figure it out.

is it possible for the boost sensor to go bad causing the computer to get confused?

how much vaccum should the system be making?

i went ahead and ordered a new n75 but it wont be here til next week. and i'm pretty sure its not the issue.

any ideas would be greatly appericated.

thanks for taking the time to read this .
 

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In all likelihood your N75 is fine... Try working the VNT (not wastegate) actuator by hand until you get a full range of motion - closer to an inch than 1/2 inch... You're on the right track...

Yuri
 

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Vnt's, waste gates lol, I can never tell which car has what. Mine has a waste gate and I went ahead and took it off anyway and cleaned it. I would do the same on your car but I'm like that I guess and yeh it is controlled by vacuum but if it's sticking it wont give it's full range and if it deviates the ecu will just stick it in limp mode I think.
 

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Discussion Starter #5
i got under the car this time and felt the actuator again it is closer to a inch id say proly 7/8 inch

i ordered a maf a map sensor (boost pressure sensor) and a new n75 i will replace them on tuesday when they get here if not i guess the turbo is coming off.....

i'm assuming that even if there was a leak in the boost hoses that the car wouldnt throw a ce light at idle.. i could see it happening at higher rpm but not at idle.... correct me if i'm wrong
 

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Discussion Starter #7
that was my thought so i'm assuming i dont have any leaks. after replacing all the sensors if i still have the problem i guess i will have to do a leak test.
 

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Yes, you can do anything really, all you have to do is seal the intake and put compressed air in. I just use a heavy duty piece of plastic over the air intake hose.
 

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VAG Error Code: 17958

EOBD II Error Code: P1550

Fault Location:
Turbocharger (TC) pressure - control difference

Possible Cause:
Intake/exhaust leak.
Hoses interchanged/not connected.
Manifold absolute pressure (MAP) sensor (G71).
Turbocharger (TC) wastegate regulating valve.
Turbocharger (TC) wastegate actuator.
Turbocharger (TC).

As taken from my http://www.myturbodiesel.com/forum/f9/free-eobd-ii-error-codes-software-2919/ ;)
 

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Discussion Starter #12
SWeet. I was thinking either maf or boost sensor ( im assuming its the same as map sensor). So i ordered both yesterday. Should be here by wensday ill let yall know how it goes.

I assumed it was one of these two sensors because it gives the p1550 error and limp mode even at idle. So im thinking it cant be a leak because at idle theres not enough air flow to make a difference i wouldnt think. Am i correct in my assumption?
 

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hy . i had same problem. presure diference. the last think i did after checking all the stuff you did,it was removing the down pipe.turbo was boosting but was no where to go, thanks to a clogged catalitic.is worth the try.remove the 3 screws from the exhaust manifold and youll find right out.
 

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Have you solved it yet?

I have a very similar problem with my car so maybe you can figure it out for me. When you were checking the turbo to see if it was stuck, was there any resistance at all? Mine does have some resistance, since everything was still hooked up I figured there should be. Mine also has about an 1 inch of travel. I did check the Cat and it's not a problem. Car occasionally has the 1550 code.
 

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Discussion Starter #16
My car had 3 problems

Their were bare wires going to the map sensor that were touchingc

I had boost leaks

My n75 was going bad
 

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Discussion Starter #18
JusT remve it. Its pointless on a diesel anyway. Your most likley cause is a boost leak , failed map sensor, or maf sensor id go ahead and clean the intake too
 

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Went for a drive yesterday. At about 2200rpm in third gear I feel a surge of power for about a second, it was doing it again today. I did get 1248 code and 1550 codes yesterday and 1550 today but not the 1248 so far today. Still has no power. Has free rev rpms to 4500+.
 
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