Newbie + 06 brm pd st-st-stutter issue. Egr?

Firstly, I'd like to say my hellos to everyone here. I've been browsing this forum since before I purchased my first TDI back in November 2010. A 2006 Jetta (Canadian Highline) with 210,000km. The reason for the high milage purchase was price for one and partially the options (mem. seats. MFD+, steering wheel controls, Rear sunshade) but mainly, after searching high and low (2009 models inclusive) this car had been meticulously maintained in both appearance (at least as far as canadian winter driven cars go) and mechanical aspects. The previous original owner had all of the VW dealer performed service records. Now that being said I realize that even so that is not enough in some cases, but after looking over the car on two separate occasions, and taking the price and options into consideration, I decided to go with this vehicle. I'm now at 243,000 km (~150,000 Miles) and still happy with my choice. The car runs very well and is still in great shape, withholding a couple of issues.

Although I'm relatively new to this seemingly more complicated TDI world, I have been working on all things mechanical since I was old enough to ride my first dirt bike (and quickly learned that if you want to ride/drive something, inevitably you will need to fix it) After highschool I worked professionally as an auto mechanic for 5 years, at which point I went back to school for mechanical engineering. I'm now in a career as a mechanical designer for companies who make automated assembly/welding machinery for the automotive industry. So though I'm far from an "expert" I'd like to think my mechanical aptitude is above average. I've tackled just about every job you can name on a vehicle from a complete restoration (94 BMW 325iS, still in progress.lol) to engine swaps to regular maintenance as in timing belt on 04 A4 Quattro. Anyways, enough about me and onto the issues at hand.

Like I said, the car seems to run great expect for one thing. It has this stutter that comes in at around 1800 RPM, which seems to be more pronounced in 1st and 2nd gear. For example as you take off from a stand stand still, ease out of the clutch then get on the gas moderately, you can hear the turbo building boost and then as comes near 1800 RPM the car stutters as if that throttle plate before the EGR valve assembly is closing and opening a few times within a couple of seconds. Then a big puff of black smoke and off she goes with gobs of torque through the rest of the revs. If you rev it out to 4000 RPM (which I don't practice doing too often) and get into the next gear then you avoid that 1800 RPM spot and the hesitation is not felt in the following gear. However it does do something similar in 4th and 5th gear (again at that magical ~1800RPM mark) if you're cruising along at a steady speed, not accelerating nor decel, but if you go from a slight decline to incline (as in the load on the engine changes) it will "buck" a few times and then you hear the turbo build boost again and all is well. Both of these situations can be helped (which I've learned to do overtime) if you "feather" or slightly "pump" the gas pedal. As if you had a nervous twitch. easier to do when going from stopped start with the stutter as opposed to the buck in 4th and 5th. I've been chasing this issue since after I bought the car and seemingly so has the previous owner as I can see by the brand new shiny EGR valve assembly (probably replaced under warranty since there was no record for this ) I've done such things as check for the VNT valves movement (seems to be fine) Replaced the N75 Valve, Unplugged one at a time and both the EGR valve and "throttle flap" plugs with no success to the issue at hand. I believe this "flap" I keep referring to is the Anti-run-on valve? One thing I have noted overtime while searching for the cause is when I turn the car off You can hear that flap (or could be the EGR itself) cycle a bunch of times. Which reminds me I guess I should take the intake boot before that off and have a look to see if it is in fact that flap. I'm not sure if this is supposed to be or if something in the electronics is telling the EGR system to cycle a bunch of times,

I could probably go one describing the little details I've noticed and think may or may not be related to this problem but I'll stop here and let you guys have a read at what must be a novel by now.

Thanks for taking the time to read and any input or suggestions is appreciated. Also I look forward to many more (hopefully shorter) posts on this forum

Cheers!
Andre

Look s like you are pretty well versed in what is going on. I was going to suggest you first unplug the EGR electrical connector, drive a bit and see if the problem goes away and if not, plug the EGR connector back in and then unplug the throttle housing (plate) electrical connector. Without the electrical connectors plugged in to these two items, their default position is open.

Upon shutdown, the throttle plate should snap shut and after a few seconds should open back up. It is odd you are hearing repeated sounds from it on shutdown. Its internal gearing is plastic and mine recently stripped out its gears and I had to replace it (it is not servicable). I opened it up (pried its crimped cover off) and the gears were stripped clean out! It was very apparent in my case, because I heard this nasty gear stripping sound after I turned the engine off as the ECU continually attempted to get the electric motor in the throttle housing to make the throttle plate to close (there is a position feedback sensor in the throttle housing to indicate to the ECU where the plate is at in real time).

If you need to replace the throttle, I think Malone Tuning has them for the BRM (the one for my BEW is different) and for real cheap. Someone posted this, but I presently don't see it on their web site. You may need to call them:

http://malonetuning.com/

If it was not them, it may have been Kerma TDI:

http://www.kermatdi.com/servlet/StoreFront

If the above is not the problem, I would install a boost guage and monitor it. Could be a turbo or turbo VNT system problem. From what you describe, you appear to have lack of air issue when the falter occurrs.

--Nate

I was thinking along the same lines as you Nate, in realizing theres a lack of air issue when the fault occurs because yes it will billow black smoke for a few seconds while its stuttering. Especially off the line, as I can see by the the disappearing-car-behind-you act. lol
I have to admit . I have knowingly just put my foot down of the line to make it stutter and feed the Jack behind me, who was probably driving like a Jack at some earlier point, a disgusting amount of black smoke.

I was also considering a boost gauge, for diagnosing this issue and for just daily monitoring while driving. can never have too many gauges But I was stuck on which one to get. lol Ever the case when it comes to cars with me. Has to be functional AND aesthetically pleasing... to me. lol I was looking at a dual steering while column mount from ECStuning but it looked kind of cheap. And I'm not sure how I feel about the dash pod for above the center air vents. I should make a decision sooner or later as a boost gauge could tell me a lot about whats going on. Either way I would be expecting to see a big boost fluctuation when this occurs. whether a rise or a drop would at least tell me more than i know now.

So about this throttle plate position sensor, where would I find that? I'm guessing that if this is faulty then it might cause some of these issues.
I've been contemplating this VAG COM software cable deal. The more I read up on it the more I feel I should have this in my tool box as it makes working, tuning, and diagnosing these cars (and Audis, Which I love all....almost) I'm thinking there must be parameters in there being logged regarding this throttle plate sensor and what occurs when it stutters. If so then I should really get on the VAG COM locater. Apparently Wingnut is nearby and has this tool.

Just realized I left this as one of those annoying unanswered open threads. I did find a similar thread called something along the lines of "black smoke no power under 2000 rpm" which basically had similar symptoms to what I was having and my solution came from the information in that thread.
So to close this, the issue with the stuttering / bucking / hesitation below 1800-2000 rpm was due to the turbo VNT vanes staying closed to long. The fix was to adjust the stop screw for the VNT actuator by turning it clockwise 1.25 turns from the underside of the car. There is already a good write up so please be resourceful and search.
But yes I know, how can such a small adjustment be the cause of such a problem? I assure you it's possible. I chased this problem by replacing EGR valves. N75. Throttle shut-off valve to no avail. I also know some will ask how is this possible for such a thing to come out of adjustment. I believe it's due to the vacuum actuator becoming weaker with age and therefore not pulling on the vanes as early as it should and then they stay closed and "bogg up" the turbo, then as they open under more pressure you get a surge with some black smoke because of the excess fuel as a result of lack of air and then of she goes.

Hope this helps.
Cheers