bnl107

As you may remember, I posted about my boost issues last week. The boost comes in surges as I accelerate at 1/2 (normal, not WOT) throttle. The needle on my boost gauge will slowly move back and forth from about 5psi-15psi, matching the cars non-linear acceleration characteristics. It is physically noticable as well since the car slightly bucks as this is happening (I feel it, although my passengers often do not). Furthermore, I can hear the turbos spool-up, then down, then up again along with this boost fluctuation.

Of course, I figured it must just be a boost leak, so I pressure tested the system, and figured I had the problem pinned down when I found a large crack in my passenger's side intercooler input pipe. I bought a set of like-new replacements from another AW member, and was expecting the problem to be gone when I finished installing the new IC two days ago... I was wrong, its still just as noticable as before.

The pressure test did not reveal any other leaks. I'm thinking of replacing my 710n diverter valves to see if that makes a difference, but I doubt it will since I don't have any "BOV-like sound" when shifting.

Any ideas of what I should look at/replace? I'll try to get some VAG-COM graph runs this evening. Could these problems just be the symptoms of my turbo breathing their last few breaths before dying? I don't have any DTC's.

Any help would be very appriciated. Thanks in advance.

ryans4

Does it happen at WOT?

Some hesitation on occasion in GIAC chipped cars is not abnormal. I had it usually only at part throttle, and in higher gears (or at higher speed, whatever makes more sense).

But it was always fine at WOT...

bnl107

... GIAC hesitation because I've had the chip in for a couple months now, and only recently began experiencing this problem. To answer your question though, yes it is only at part-throttle (WOT throttle is smooth).

ryans4

...i'm at a loss. N75 Valve? Most sensors (thankfully) through a DTC so you kind of know what's going on.

RKA

Have you pressure tested after fixing the IC?

bagodoosh

try going into engine adaptation channel 0 and resetting them.

Swank4

Just throwing this out there - what about a bad N75?

bnl107

I was having some hesitation at WOT (I figured it was throttle-cut), so I installed the MBC. Shortly after that I began noticing this new hesitation at 1/2 throttle. Not sure if it was there before the MBC install or not, but the MBC did seem to stop the WOT hesitation. I am thinking of taking it out to see how the car runs without it, but that would be a rather in-depth task after having to splice the N75 related hoses to run it in parallel. I have quadruple-checked everything, and I know it is installed correctly. What would cause this problem that would be related to the MBC (AFAIK, the MBC wouldn't even function at 1/2 throttle, it would only kick in at WOT when there was a spike, correct?)

What would resetting the engine adaptation channel do? I haven't heard of that procedure before.

bnl107

Yes, no apparent leaks.

ryans4

pull the MBC out and put it back to normal N75 only and see if problem is still there...