[Vwdiesel] Overboosting Problems

[Dave Cook]

My buddie's '01 Jetta TDI keeps "overboosting" and throwing the following code:

16618 - Boost Pressure Regulation: Limit Exceeded (Overboost
Condition) 
        P0234 - 35-10
-  -  - Intermittent
Sometimes it'll turn on the check engine light and sometimes not, but it will go into limp home mode, which is really frustrating on the freeway.  Sometimes the check engine light will be on without being in limp mode, but it is because that code was thrown.  It won't go into limp until it actually overboosts, or whatever.

Here's what I've done/tried:

I pulled the vacuum line off the boost pressure valve and sucked on it, I was able to get the actuator to move down by the turbo, and it held it's position until I released vacuum.  

Verified plenty of vacuum is reaching the boost pressure valve.

The boost pressure valve was installed new this past spring.  With my vacuum gauge, I saw that some vacuum was passing through it at all times, even with the engine idling.  I swapped in the old valve and it did not pass vacuum at idle.  Which is right?

While driving, I tried unplugging the MAF to see what happened, and it made no difference other than slightly reducing power (which was further reduced when it went into limp mode while going up a hill).

Is there any way to test the boost pressure sensor?  I believe it is down on the intercooler.

Other ideas?

 
Dave Cook