[nozzleman]

I have read everything on this forum about this problem and am now more confused than I was before I started. I bought this car less than 2 weeks ago (already regretting it) My car has 77k on it. I put less than 300 miles on it before I felt a loss of power driving down the freeway with no CEL(wouldn't keep speed going up hill, and took forever to get up to speed). After re starting the car I had return of power for about a min or 2. After cooling off it went another 200 miles or so before doing it again. Now today it started throwing a CEL reading engine overboost condition. I originaly read and thought mabe the MAF but after further reading here I am not too sure. I am not super mechanicaly inclined and I don't know where to even start. The VW dealer here is a bunch of crooks and I don't want to have to take it there. I may try and fix it and sell it before I run into more problems (don't want to b/c I do like the car) Help please!!!

 

[chittychittybangbang]

First, go to autozone or your local parts store and figure out what codes the car is throwing. This is the best first step to give an educated guess. Then come back and post what codes you have. Your overboost is normally a bad n75 (boost control solenoid), bad n75 wiring, cracked vacuum lines, or sticking turbo.

It could be the MAF, it could be clogged intake, fuel filter, cracked vacuum lines, boost leak, it could be many things, most of which are easily fixed. http://www.myturbodiesel.com/1000q/multi/limp-mode-TDI-fix.htm Look through this article to see what the common causes of limp mode are and then go through the tests.

77k is way too young to throw away the car.

 

[nozzleman]

The code that it is throwing is p0234 engine over boost contition.

How do I check the N75

 

[fstjetta]

Did you buy it from a dealer? Maybe Indiana has a law on used cars since it's only been 2 weeks and less than 300 miles. Have them fix it.

To check the N75, unplug it and swap it with the EGR solenoid. They're both on the firewall and look similar. Check all the vacuum lines too.

 

[nozzleman]

When you say un plug it and swich it with the EGR do you mean just the wiring harness or the hoses as well? Sorry If I am asking too many questions and sound stupid but working on a car (other than routine maintence) is fairly new to me.

 

[chittychittybangbang]

Completely unplug all wires and vacuum lines and swap them for testing purposes. Make sure to read the limp mode article all the way and follow the links. http://www.myturbodiesel.com/1000q/a4/VNT-wastegate-adjust.htm Read this article on more on testing the VNT line and system.

 

[kd7iwp]

The actual valve component is the same piece of hardware for the EGR and the turbo boost regulator. So that is why you can completely unplug and swap the two (if the bad valve is swapped into the EGR system it won't affect vehicle performance). So unplug the electrical connectors and vacuum hoses on both valves and swap them and see if your limp mode goes away.

 

[Jerry King]

I have read everything on this forum about this problem and am now more confused than I was before I started. I bought this car less than 2 weeks ago (already regretting it) My car has 77k on it. I put less than 300 miles on it before I felt a loss of power driving down the freeway with no CEL(wouldn't keep speed going up hill, and took forever to get up to speed). After re starting the car I had return of power for about a min or 2. After cooling off it went another 200 miles or so before doing it again. Now today it started throwing a CEL reading engine overboost condition. I originaly read and thought mabe the MAF but after further reading here I am not too sure. I am not super mechanicaly inclined and I don't know where to even start. The VW dealer here is a bunch of crooks and I don't want to have to take it there. I may try and fix it and sell it before I run into more problems (don't want to b/c I do like the car) Help please!!!

Sounds like a MAF problem , unplug it and see if it runs better ( it will throw a code when you unplug it) or find someone with a VCDS code reader and ask them to check it for you. Some Autozones will read it for you but they only have generic code and will not always give you the right code. Your can check over on Fred's TDI Club for a list of people that have the proper software and will help you find your problems.

 

[nozzleman]

I am going to swap the EGR and Boost regulator to see if limp goes away. Problem is that I may have to drive 100 or so miles before it goes into limp mode again. Is this ok? That is what makes this problem so hard, I may drive it a week or so with no problems then all of a sudden it goes into limp mode. Once in limp mode I can turn the car off and back on and it will go away for a min or 2, then goes back to limp mode. After I let the car cool all the way off it runs (sometimes for a day or 2) a bit before going into limp mode. Am I going to cause any problems by swiching the egr and turbo boost regulator for a 100 mile or so drive?

Also when in limp mode if I unplug the MAF the performance doesn't change so I assume there isn't a problem with the MAF?

Thanks again

 

[chittychittybangbang]

Answers in bold

I am going to swap the EGR and Boost regulator to see if limp goes away. Problem is that I may have to drive 100 or so miles before it goes into limp mode again. Is this ok? That is what makes this problem so hard, I may drive it a week or so with no problems then all of a sudden it goes into limp mode. Once in limp mode I can turn the car off and back on and it will go away for a min or 2, then goes back to limp mode. After I let the car cool all the way off it runs (sometimes for a day or 2) a bit before going into limp mode. Am I going to cause any problems by swiching the egr and turbo boost regulator for a 100 mile or so drive?

no

Also when in limp mode if I unplug the MAF the performance doesn't change so I assume there isn't a problem with the MAF?
when you unplug the MAF the performance should go way down since the ECU falls back to a safety setting. If it's unchanged you know the MAF or wiring is bad.

Thanks again
no problem, feel free to follow up with anything you don't understand but please make sure to read all the links for troubleshooting so that you ask the right questions

 

[nozzleman]

Reading the MAF 100Q it doesn't sound like my vehicle. It states that "If power is restored by shutting the car off and turning it back on, you are in limp mode and the MAF is probably not the main contributor to the power loss"

If I shut off the car and turn it back on it does correct itself for a few min.

When the car is in limp mode and I unplug the MAF and nothing changes is a sign that the MAF or wiring is bad?

Should I begin by changing the MAF?

I am looking for advice and have gotten a lot of it now I just need to know where to begin?????

I am lost!

 

[chittychittybangbang]

Sorry, I should have been more clear, I will add these notes to the writeups. When the car is in limp mode the unplug maf check won't work. It only works when the car seems to be running. Can the MAF cause limp mode? Possible but it shouldn't. Normally the MAF causes constant low power.

Have you checked ALL the vacuum lines, tested the VNT actuator stickiness, and done a boost leak check? These are good places to begin.

 

[nozzleman]

Update

I Swiched the N 75 and the ERG last night. After a few short trips the CEL went off on its own and it didn't go into limp mode(I am not going to get my hopes up) the real test will be the drive to the lake on saturday night.

I did notice the temp gauge would drop to cold then slowly work its way back up to 190 (which is where the car usually runs). It did it twice last night not sure if it is related or just a fluke bad wire but I wanted to mention it.

Thanks Ill keep updated on my progress

 

[chittychittybangbang]

It's probably a bad coolant temp sensor or plug, common problem, probably not the thermostat. Look on the driver's side coolant flange coming off the head. There's a coolant sensor, possibly green. On a cool engine, unscrew it. Coolant will come pouring out. Screw in the new sensor. Top off the coolant with new G12/distilled water mix. Do not use green prestone, G12 isn't compatible with it.

 

[xaeryan]

I have fought with the same code being thrown. It's 99% not the MAF. As chitty said, the MAF would result in constant low power. They tend to go bad gradually, but not intermittently. If you haven't already, swap the solenoids as mentioned. EDIT: oops, I see you did this already. Find yourself a nice long steep hill and go up it using full throttle (within safe limits) in a higher gear. That's about the most you can load the car to test.
Other causes for overboost that I didn't see mentioned much here include EGR / intake manifold clogging as well as VNT actuator mis-adjustment. I believe the latter is my problem, as I adjusted my (new) actuator to the same length as the old one, which was rusted solid, but I have a good feeling that this adjustment wasn't right. Also, the vanes on the turbo could be sticking preventing the arm from fully releasing, but I don't know how likely this is (I suppose not too farfetched, as if there is a clog preventing ONE vane from "opening" fully, it would prevent all of them).
Chitty can chime in more I'm sure.

But don't give up on it, especially with that low of miles. If it's happening frequently and you need to drive around it, you can plug the topmost line going to/from the N75 solenoid. This will prevent the turbo from building much boost (particularly in low RPM), and might keep you out of limp mode. The car is sluggish like this, but nothing compared to limp mode!

 

[nozzleman]

UPDATE!!

I drove it to the lake this weekend and back with no problem. I don't feel out of the woods but its looking a bit brighter. I am giving it another week and then ordering a new turbo boost control valve. Where is the best place to get one?

Thanks

 

[Blackcat]

Dealer, worldimpex, 1stvwparts, autohauzaz