2001 Jetta TDI boost issues...did a lot of searching, cannot find this snag

e300d · Sep 1, 2011

Hello,

Recently I have had boost issues on my ALH ....

Did the troubleshooting as per the instructions here and so on....

I did the following checks:
MAF ok

Vacuum hoses and good suction present.

Replaced VNT actuator as it was not holding vacuum and lots of rust inside of it.

VNT lever moves freely.

Swapped EGR N18 and N75 valve and no help...

Opened up N75 valve and lubed it, a lot better now....

Went out and got another functioning N75 Valve...

Now I have boost 1 out of 2 starts. Meaning:

If I start the car, it has no power.....I shut it off for a sec and all boost comes back and stays for duration of the drive......

I shut it off again and restart..no boost.....2nd restarts and boost comes back

I do have CEL all this time. No I did not scanned it ( bad move i know)

My question is: is this ECU problem now, do I just reset the CEL light via vagcom ?

Has anyone had a similar issue ?

Thanks

Super T · Sep 1, 2011

Sounds like limp mode. You really need to see what the CEL is. That should have been your starting point. Find out why the light is on and go from there.

ruxkii-aces · Sep 1, 2011

i have a similar problem thats started 2 days ago, except mine stays in limp mode every start and i have no CEL. i had limp mode problems before but they always came with a CEL and a restart of engine always got rid of them. this time it wont go away and there is no CEL. any idea what the problem could be?

e300d · Sep 1, 2011

Super T said:
Sounds like limp mode. You really need to see what the CEL is. That should have been your starting point. Find out why the light is on and go from there.

You are absolutely right .

The reason why I got a new actuator is because after testing it, it did not hold vacuum, was all rust inside with crap falling out of it. I thought this would be the culprit....Besides from what I gather scanning the car would give me either over/under boost.

I figured since I am seeing underboost, and the VNT actuator does not hold vacuum, it would be it...

Anyways, does anyone ever experince multiple system failures that lead to limp mode?
Such as faulty VNT actuator and some other component that is also failed?

Also, does the CEL goes away on its own if the issue is fixed or do I still need to reset it so that the ECU has the right parameters ?

Thanks again, when I get back from work I will definately get the car scanned.

rdkern · Sep 1, 2011

Many times you need to reset the code - or it never goes away. The CEL may turn off after a number of start cycles, but that varies for the code and car, and I don't have specific knowledge of yours.

I also suggest getting a scan. What you describe is very odd. I have not experienced, nor seen here, any problem that happens every other key-on. I can see something being more random, but not every other key-on.

The scan might help. Having the scan tool handy when you start it might also help. After all, if it's a "limp mode issue", the cause should be findable. If it's an irregular electronic glitch, it does become challenging.

And others have experienced multiple system failures that led to limp mode. When one item in the boost regulation system goes down, others often follow. For instance, a bad N75 would cause the vnt actuator not to move, so it sticks. In such a situation, replacing the N75 timely would have fixed the problem, but replacing it after several months might not.

e300d · Sep 1, 2011

rdkern said:
Many times you need to reset the code - or it never goes away. The CEL may turn off after a number of start cycles, but that varies for the code and car, and I don't have specific knowledge of yours.

I also suggest getting a scan. What you describe is very odd. I have not experienced, nor seen here, any problem that happens every other key-on. I can see something being more random, but not every other key-on.

The scan might help. Having the scan tool handy when you start it might also help. After all, if it's a "limp mode issue", the cause should be findable. If it's an irregular electronic glitch, it does become challenging.

And others have experienced multiple system failures that led to limp mode. When one item in the boost regulation system goes down, others often follow. For instance, a bad N75 would cause the vnt actuator not to move, so it sticks. In such a situation, replacing the N75 timely would have fixed the problem, but replacing it after several months might not.

Thanks for your reply.

Today driving to work, it started in limp mode, I shut her off and it never went to have boost. Now it is stuck in limp mode....

To recap:

replaced vnt actuator
replaced n75
tried 3 different mafs to see if it is any better

Gotta scan the car now for sure!!

rdkern · Sep 1, 2011

If it's underboost, look at intakes. If overboost, you may need to take a drive with VCDS for me to even guess.

e300d · Sep 3, 2011

rdkern said:
If it's underboost, look at intakes. If overboost, you may need to take a drive with VCDS for me to even guess.

Got scan today and got P0106 - Manifold absolute Pressure / Baro Sensor Range/Performance...

MAP sensor ?

e300d · Sep 4, 2011

e300d said:
Got scan today and got P0106 - Manifold absolute Pressure / Baro Sensor Range/Performance...
MAP sensor ?

Went and checked the wires to MAP sensor, put some dielectric grease on connector and car is running great now.

rdkern · Sep 5, 2011

Glad you found an answer. Let's hope this is a fix. Electronics.... can't live with them, can't live without them...

Super T · Sep 6, 2011

Glad you found it! Always scan first when you have a CEL! It will point the way! Usually

dilkie · Sep 7, 2011

here's a dumb question. I had the same code and went to look for the MAP sensor and came up empty. Where is it located? I assumed somewhere on the pressurized side of the intake manifold but I couldn't for the life of me find the darn thing.

AndyBees · Sep 7, 2011

The MAP (Manifold Absolute Pressure) sensor is located on the pressure pipe coming off the Intercooler just behind the right head light.

Start at the EGR.........follow the black rubber pipe to the black plastic pipe going toward the back of the right head light. Along the side of that black plastic pipe you should find a wire (in the black cover). Follow the wire (two of them inside) and it will lead you to the MAF sensor!

EDIT: Seems some ALH models the sensor is actually on the Intercooler, top side of course! Some models it is located on the pipe that comes off the IC, top side of course!

Right head light instead of left ................too much Crown Royal!........LOL

dilkie · Sep 9, 2011

thanks! I would never have found it.

Wow... I needed flashlight just to get a peek at it, on top of the intercooler.

So, how does one go about replacing the MAP? Remove the headlamp? If so, it looks to me like it's the two screws on top plus removing the front grill.

Or do you remove the intercooler?

BlownBusa · Sep 9, 2011

I think I just moved the washer bottle.

dilkie · Sep 12, 2011

BlownBusa said:
I think I just moved the washer bottle.

and the fuel filter... got it... thanks.

unfortunately, my woes continue, both screws snapped off so out came the whole intercooler so I could drill out the bits left in there. And I decided to wash the thing since it's out... thunderstorm came up, left it washed and drying and will do the screw stud crap extraction/drilling/swearing thing tomorrow.

Bet after all this that the MAP isn't my problem anyway...

cevans · Sep 12, 2011

dilkie said:
and the fuel filter... got it... thanks.
unfortunately, my woes continue, both screws snapped off so out came the whole intercooler so I could drill out the bits left in there. And I decided to wash the thing since it's out... thunderstorm came up, left it washed and drying and will do the screw stud crap extraction/drilling/swearing thing tomorrow.
Bet after all this that the MAP isn't my problem anyway...

Nah, if you've got a code for the MAP its pretty clear thats the culprit. Driving with the MAP unplugged yields instant limp mode FWIW, so the intermittent-ness of the limp mode corresponds with the intermittent connection.

MAP Screws snap on...I think its 115% of intercoolers.

e300d · Feb 15, 2012

cevans said:
Nah, if you've got a code for the MAP its pretty clear thats the culprit. Driving with the MAP unplugged yields instant limp mode FWIW, so the intermittent-ness of the limp mode corresponds with the intermittent connection.
MAP Screws snap on...I think its 115% of intercoolers.

Update- car still runs good...knock on wood lol

thermo · Feb 16, 2012

me too?

Symptom: Occasionally, I would experience loss of boost - car just won't go. No CEL codes. I replaced the N75 valve a month or so ago. Didn't experience anything that seemed bad after that - until recently.

The symptom came back - but last night, it was really weird.
While driving on the highway, at more or less constant speed, the boost was surging - and by that I mean one moment it was not there and the car felt sluggish - and the next moment it was there and the car felt strong.
Light acceleration confirmed this - boost & acceleration, then nothing, then yep, it's back. Really weird.
Stopped at the grocery store, and when I restarted and headed home, it was good again.
This morning, under acceleration to get up to speed on the on-ramp, it underperformed a bit, but nothing like last night.

I suppose it *could* be a vac leak. I replaced the turbo actuator a couple years back so it *should* be ok.

Thoughts?

2001 Jetta TDI boost issues...did a lot of searching, cannot find this snag

e300d

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Super T

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ruxkii-aces

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e300d

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rdkern

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