98 TDI Limp Mode - Boost on, Boost off, Boost on?

Hey, so I'm literally in the beginnings of getting ready to fully restore this TDI (I'll make a thread here). It's a real piece of work right now, but I'll leave that aside.

I have limp mode on the motor and am super busy with school so I have been trying to troubleshoot (as I can go over to the border once more to get parts - which saves me HUGE $$ in Canada) - so I am trying to troubleshoot it before hand so if I need anything, I can save some coin. I will have a Vag Com coming, but that will be the last time I can go to the US.


DESCRIPTION OF PROBLEM
I'll be driving and it will boost just fine (until about 2.5k rpm), UNLESS any load is on it (going up hill) or I am in a higher gear - it will cut off the boost.

If I keep it floored (or accelerating) the boost will go "on-off-on-off-on-off" back and forth, up the rpm range.


After looking through TONS of limp mode threads, I haven't seen someone quite explain it like this. I have replaced all vacuum lines, did a new o-ring on the fuel pressure regulating valve, put a new air filter, and am going to put in a new fuel filter (though I doubt that is the problem, I've drove to the point of a clogged one before - I don't have a sudden loss of all power 100% of the time). N75 and MAF have been replaced in the last 2 years. Last year, EGR valve and intake was cleaned.

From what I can gather - the WG may be stuck closed and this overboosting is causing the ECU to limit boost, but why would the boost come back? I'm not sure what to think.

ALSO it gets a real heavy diesel smell at start up.. my other TDI's were not like this. I suspect a potential exhaust leak?

I won't be able to pull the turbo or get under there well until I get ready to tear the whole thing apart.. But if anyone has any direct experience with these symptoms and knew what it was - I would appreciate the info!

Maybe it will help the next guy.


CODES THROWN:
00575
00560
01117 <-- ( DC load terminal, or alternator)



Thanks guys. Just trying to save one more MK3 from the scrappers! Got a soft spot for these rust buckets..

It's your EGR faulting, not limp mode.

The EGR is opening and closing, and the car is equilibrating what it sees for airflow through the MAF. So either the EGR weep hole is plugged not allowing the diaphragm to reseat or the valve is opening and closing, probably due to a bad N18. I've seen it before.

It's yet another reason I advocate tuning out the EGR and blanking it off.

You just saved me a lot of monkeying around.

Deleting the EGR would be ideal and easiest route, I'm sure. I'm just not sure I want to do that considering the effect it has on the environment. I'm kind of passionate about that stuff.

I'll take it apart and see what I can do, maybe I need a new manifold and for the time being maybe I will have to block it off.


Appreciate the input Abacus.

My only next question is - since this is a non-functioning or EGR problem, would just a simple block off plate do it? Or would I have to chop off the whole valve and replace it with new silicone tubing or something of that sort?

Thanks.