Irregular boost (higher than requested)

I've had this problem over about 2 years and it seems to be getting progressively more common.

At highway cruising, I normally boost around 5 psi. The problem is that my boost will go up to 10 psi for no apparent reason. Usually it goes up on gentle downhills but now it also does it on flat ground. Usually it drops back to 5 psi on gentle uphills.

Logs reveal that during these episodes, the requested boost stays the same but the actual boost pops up, corresponding to the boost gauge. The vnt duty cycle goes up too. So there is some kind of controller issue I assume. Unplugging the ASV changed nothing. Unplugging the EGR or the vane position sensor actually make the spikes worse, going up to 15 psi.

There don't seem to be any damaged wires or vacuum tubes. Another member had virtually the same problem and it turned out to be frayed vane position sensor wires but mine look fine form what I can see.

My egr duty cycle seems to be stuck at 100.6% most of the time. Could the vane position sensor be bad? What does this control exactly? Is there any way to test it? Do you need to get a whole new vacuum actuator assembly?

Any help would be appreciated. I think I am decreasing the life of the turbo when running it at 10 psi for long periods when it should be at 5 psi.

Ran some more logs. Turns out the egr seems to be opening during these boost "spikes". Duty cycle goes down which I assume means the egr valve is opening since at idle and during hard pulls it stays at 100.6%

Also, the charge pressure cycle goes up, which I assume means the vanes open, since at idle it's at it's max and during hard pulls it goes down. So for some reason the egr valve is opening too much during cruising or the vane actuator is not moving far enough.

Arrghhh.

Increased EGR flow should decrease turbine energy, all else being equal.

The increased N75 duty cycle means it's delivering less vacuum to the actuator, to reduce the pressure. The smart actuator position % should decrease as a result.

Immediately before the boost spikes occur, does the smart actuator position ever increase?

Since I haven't worked with your type engine, I have reservations about making too many comments about it.

I can't find a block to measure the smart act. I'm not getting any faults but when I go to the "Readiness" section in VCDS under the engine controller, it says egr failed or incomplete. I did the output tests and everything seemed to check out fine although I'm not really sure what it's testing for.

Any advice is helpful since I feel like I'm not really getting any closer to any solution.

Supposedly it's in group 43, value 2, at least for BEW. You could try mapping the controller. For some reason I initially thought it would be right there in a charge pressure control block.

That is probably normal. The ECU checks the function of certain items during certain conditions, it may be when it is running the EGR flow test that this happens.

Generally so long as the ECU is able to control boost, and no faults are triggered and all the readiness stays set you should be good. However, one common spot on the BEWs is the vacuum line to the VNT, down in the firewall area, can split. That usually causes a loss or low boost, and will set a DTC. But the way they rub through, it is plausible that the hole in the hose is momentarily sucked against the air intake tube to which it is attached. This could, possibly, cause an up-and-down duty cycle on the N75 as the ECU tries to equalize.

Since your EGR duty cycle is changing when this happens, I suspect maybe the EGR flow is being tested. I have never driven a BEW with a boost gauge for any length of time to know what is 'normal' or not. I do know a lot of people here start chasing problems they think they have based on what an added-on boost gauge is or is not doing, only to find out everything is working properly. You may want to compare to another identical car.

Since your EGR is failing readiness, it should be setting a DTC before too long. I put a LOT of EGR valves on BEWs and BRMs lately, but they always have a fault.

One quick check of the EGR:

find the appropriate Measuring Group (I forget which one right now, maybe 002?). It will be labeled RPM, MAF requested, MAF actual, EGR duty cycle. At a warm idle, after reving the engine, the EGR will be on, and the DC should be up some (over 65% or so generally) and the MAF actual should closely match the requested. Let the engine sit and idle. After about 90 seconds, the EGR duty cycle should drop (never to 0, but maybe 10% or so) and the MAF actual should jump up, nearly double the requested.

Hmmm. In town driving doesn't seem to be affected or I don't notice because boost fluctuates anyways. I never seem to have too low boost. I checked all the vac lines and they are in good shape. I took the ASV off and looked at the egr and intake and there is very little soot in there (yay ULSD!).

I'm a little confused with the VCDS units though. It seems on mine (BRM), the egr is closed at 100.6% and open as it goes down. And the n75 seems to close the vanes as it goes down. My egr flow seems to constantly flow. Something like 500mg/st at idle for both requested and actual. I would think that at some points it would be zero wouldn't it?

I will try the idle test.

My egr cooler valve doesn't seem to have any excessive soot around it. And no whistling or whooshing at idle while under the car.

If I unplugged the EGR, will it stay closed? Because unplugging it didn't seem to affect the condition, actually it seemed to boost to a higher point. Would the EGR opening cause the boost to rise from the exhaust manifold pressure?

This is bugging me because I commute a lot and the turbo seems to be boosting too high over half the time while cruising on the highway.

Nearly 2 years later and still present. I have nearly resigned myself to the possibility of this being normal behavior. However, it still bugs me that the turbo life may be being shortened by spinning the turbo faster than necessary for long periods of time on highway commutes.

Anybody have any new input into this?

2005 Passat TDI, 5-speed.

I've read all the EGR comments here...No answers.
My MAF is not showing weird behavior tho...
The EGR = 100.6% never changes no matter what the throttle position is...I blip it up to approx 2000 (as long as I can stand the vibration (see another similar post!) and it does not change.

I read OILHAMMER's comments but don't see a resolution to whatever the problem is yet.

What happed, happened pretty suddenly...I suspected a load of poor fuel, but after running the VCDS and finding the EGR reading and reading all these EGR psots. I suspect it wasn't the fuel.

Yo~! OILHAMMER...whatcha say?