[Vwdiesel] Limp Mode Frustration

[Tad]

It would be interesting to see actual pressure readings from a
mechanical boost gauge.  I tapped mine into the plastic pipe just
upstream of the 90-degree bend leading into the EGR.

Assuming the overboost codes are genuine, I'm with Hayden about the
VNT being the root of the problem.  Over time the VNT gets clogged up
with soot (especially if one doesn't "exercise" it regularly) and the
issue gets worse as the VNT movement gets restricted.

Some have had luck cleaning the VNT mechanism on-car with Seafoam or
other products or by removing, disassembling and cleaning.  I believe
the only "official" remedy is turbo replacement.

As Hayden said, a clogged intake exacerbates the problem (think
blowing through a very small straw).

You mentioned the head gasket - why did this get changed?

On Sat, Mar 3, 2012 at 7:43 PM, Dave Cook <davevw at yahoo.com> wrote:
> This is a friend's '01 Jetta TDI.  Keeps going into limp mode, sometimes with a check engine light, sometimes without.  Has been this way for a
> long time.
>
> Last spring, I replaced all the vacuum lines while replacing the head
> gasket, timing belt, and a few other bits in hopes of fixing this.  Also
>  replaced the N75 at that time.
>
> Still goes in limp, and does it more often than not at this point.
>
> I decided to try some more troubleshooting today.  In doing some
> driving, I found that the ECU would show two different codes after going
>  "limp".
>
> They were:
>
> 16618 - Boost Pressure Regulation
>             P0234 -
> 35-00 - Limit Exceeded (Overboost Condition)
> 16492 - Manifold / Barometric Pressure Sensor (G71) / (F96)
>             P0108 -
> 35-00 - Signal too High
>
> They were showing up sort of alternatively, maybe a couple times one of
> them and a couple times the other.  Or a couple one, then the other,
> then back to the one.
>
> Once, both popped up at the same time.
>
> I was romping on it going up hills during this testing.  It only took a
> couple seconds of heavy acceleration to cause limp to come up after
> having shut down the car and clearing the codes.
>
> I then pulled the MAP sensor from the intercooler.  I noted a oily
> coating on it, so I cleaned it off with air flow sensor cleaner.  No
> change on reinstallation.
>
> I'm thinking the problem might be the MAP sensor, but my friend doesn't
> want to throw money at the car hoping something fixes it.
>
> Any other thoughts?
>
> Dave Cook
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