VW ALH Turbo and Vacuum Problem Determination Info

What Can Go Wrong that you have no/not much power...the engine won't rev above 3000 RPM and has no guts.

But first:

• I knew I didn't have overboost, but there is much valuable information here in the master overboost/limp mode thread that applies.
  Diagnosing and Fixing Limp mode for A4 1.9TDI [low power troubleshooting
  (In overboost, your car's vacuum system shuts down turbo operation whenF the boost pressure is too high; simply cycling the 'ignition' switch will restore turbo in that situation).  More knowledge is better!  Alas, you have to understand the system before you can chase your problems.
• ...and in order to even begin to troubleshoot this system, you need to know the bits and pieces of it. The diagram to the right is your friend, get friendly with it. There is a whole 'Bits & Pieces' section on that (with the bigger copy of the diagram) which you should probably read first. Included there are the part numbers for everything and where you can buy them.  
• This is not an overly complex system, not like the engine's computerization. When you dive down this rabbit hole and finally have the rabbit (or Golf or Jetta) running hot again, you will have two satisfactions:
• You will have mastered the engineering of your car's boost system
• ...and saved a ton of money compared to going to the dealership, where instead of replacing a few small cheap parts costing maybe $200, they regularly replace the turbo and its control system to the tune of $1500 or so
  

There are all kinds of reasons you can have little get up and go....

• Turbo problems
• with the turbo itself (I haven't run into this yet, so there'll be nothing here on that)
  
• with the turbo actuation system, which in the ALH is vacuum actuated.  It can be:
• bad tubing
• a frozen/busted VNT, which is a variable nozzle turbine pressure control (as opposed to simple waste gate). There are vanes that change how much power is derived from the exhaust gases and how fast the turbo spins.
• a bad actuator: this is a can with a diaphragm inside of it; when vacuum pulls on the diaphragm, an attached rod pulls on the pin that controls the VNT.
  
• bad control modules: electrically operated solenoid valves that control the vacuum going to the actuator
• bad check valves
• the vacuum pump (diesels having no carburettor and butterfly valve to create vacuum need a pump to create vacuum...also used by the power brake booster)
  
• Problems elsewhere (like a clogged cat or intake manifold), see here
  

Anyway, What Can Go Wrong In the Vacuum Control System

Bad Actuator

See here below

Check valves

Clogged or jammed

Bad solenoid valves

Not operating or valve(s) leaking. The valves are mounted on the top of the firewall at the back of the engine compartment, turbo controlling N75 on the right (driver's) side, N18 EGR controlling. in the middle.  The intake manifold changeover/anti-shudder N239 valve is clipped to the intake manifold a bit to the left of center

Bad vacuum lines

Hoses may be disconnected, broken, kinked.  Check carefully, better yet replace them with silicone vacuum hose

Frozen VNT

I won't address this (didn't have the problem), other than to say: if you pull vacuum on the actuator and it doesn't move, likely the VNT is frozen.

Bad vacuum pump

Pump may be failing, internal seals may be broken or leaking. Test with MityVac, search on posts for this. Seals may be replaceable.  It is a round flat tin can, rather like an oversized snuff tin on the right side of the engine block.

Problems elsewhere

Clogged Intake Manifold

The intake manifold can be full of carbonized gunk, see here for how to determine if this is the case.  If it is, you have major mechanic's work to get the manifold off the engine and then cleaned out.  Some people burn them out, Google "burning out a clogged vw diesel manifold".  As should be obvious, an engine that can't breathe doesn't have any power.

Clogged Catalytic Converter

Obviously, if an engine can't exhale.... See here.

Intercooler

Make sure that your fragile and expensive intercooler is protected by a fully intact and secured fender liner.  The intercooler cools the air fed to the turbo.  Cooler air is denser air with more oxygen.  The turbo, in compressing the air, also heats it up...basic physics..this pre-cools it.  It's on the passenger side in front of the wheel, behind the fender liner.  If the fender liner has broken free or shredded (happens a lot), your intercooler is unprotected.

There is a special RF fender line that has a grille for the intercooler available from IDparts, as are all the securing hardware.  You get extra points for checking this out and making sure it's right...an ounce of prevention is worth a ton of cure....and it's dead easy to do.

Considerations

• One person pointed out that, if you had a perforated or corroding actuator diaphragm, crap would be sucked into the vacuum system, clogging and obstructing the control valve/modules and check valves.  So a failing actuator could screw up other parts of the vacuum system!
  

Problem Determination/Analysis

1. The vacuum control system is messed up in some way. I am going to address this.  Debugging it is relatively inexpensive: the full kit of parts should be no more than $200.  It's also doable without a lot of tools and can be done over a number of interrupted days with the car drivable in between (if with no turbo)
2. The turbo or its actuator/VNT is dead OR the actuator is out of adjustment. 

#1: Checking out the turbo's vacuum control system

• Hoses: If you  haven't replaced your vacuum hoses with silicone ones, do so.  It's easy. However:
• be careful pulling off the old hoses that you don't break the nipples they're on. Maybe take a single-edged razor blade and slit the portion on the nipple lengthwise then peel it off.  There are special tools for removing hoses(search arg: hose removal pliers) for as little as $10.  Since they are made to work with small and bigger hoses, you may have to grind off some of the jaw tips to make them work for the smaller 3 & 4mm tubing here.They have two V jaws you put between the end of the tubing and the device and then squeeze to force the Vs apart and the tubing off.
  
• Replace them one at a time, so you don't lose track of what goes where.  Replace a few, then take it for a drive to make sure everything still works

• Check Valves
  
• The black check valve (#10) with a vacuum port nipple in the Brake Booster hose can stop turbo actuation if clogged.  Get a pipe cleaner (now called a "fuzzy stick"!), carefully remove the small vacuum line and gently swab down the the vacuum port.  Better yet, replace it. Be very careful of the little plastic nipple circled in red, it's fragile and essential to turbo actuation.
  Note Well: The little side nipple on #10 is the source of vacuum that runs everything related to turbo control and actuation. The vacuum pump creates vacuum for the power brakes booster (where the big hose runs to) but that little tiny nipple passes vacuum to the turbo control system: the VNT vacuum actuator, the EGR valve (#4) and the anti-shudder valve (#1)
  It appears this vale should be checkable and cleanable. The side nipple is simply enters into the check valve on the side towards the vac pump. Looking down that short pipe you can see a pipe cleaner when inserted in the nipple.  You can check the check valve by applying pressure to the long and seeing if it holds. What fluid could be used for flushing that wouldn't harm the rubber components?
  
  
• The black and white check valve (#7).  Have you checked the check valve that's in the hard line that goes from the vac pump to the brake booster for functionality?  As well, the vac reservoir stores vacuum for supplying the two check valves (N75 and N18). A weak pump combined with no vac storage wouldn't allow the turbo to be fully functional, or functional at all. But since you replaced the pump, even if you did have a leaky reservoir, it should be able to supply the needed vacuum for the turbo demand. Link  Note that the white side points towards reservoir. We call this check valve the 'ying-yang' valve; it is easy to check... should hold vacuum one way, and not the other. If it is open both ways, it's bad.
  
  
• My wild guess: check valves may be a weak link in the system: they are unpowered and if they gunk up over time and mileage (my Jetta had 260K when the turbo actuation got dodgy), they won't work or do their job badly.  I have had the #10 valve need cleanout numerous times and #7 can't be cleaned out. In my latest p0299 low power/no turbo, I had replaced the EGR#13 module, some of the hose and the #7 check valve, then took the car for a test ride to make sure that everything still worked (minus the turbo).  The turbo was back! I doubt it was #13 (which has nothing much to do with turbo actuation) or the hoses, so it might probably have been the check valve.  But several months later, the turbo was gone again.
  
  
• Replace the check valves, #s 7 & 13.  I got lucky at this point and the turbo was back.  At the point I went no further...but 2K miles later, turbo is intermittent again.
• Further Vacuum System Tests
  
• Simple vacuum check: "Here's what you can do even without a scan tool to watch the engine data:
  Verify the vacuum system is intact, starting with the source (vacuum pump). If your brake assist is normal, you can assume the pump is at least working and there may just be a small vacuum leak somewhere... but still, check the big booster tube for any cracks or splits. This is VERY common.
  If that is good, then you can start checking the system at the small nipple coming off of that big tube.
• If you didn't get lucky, it's time for real vacuum testing with a Mity Vac, so you can test the vacuum and how it changes when, at the various places of the vacuum system....Vacuum actuator checks
• First I would establish actuator movement. The failure of the actuator to move properly is the leading cause of VW turbo failures. With a vacuum pump, such as a Mighty-Vac, or the Harbor Freight clone, draw 30" of vacuum. You can access the line for the turbo on top at the solenoid on the firewall.  30" should sustain for more than 10 seconds to a vacuum of 25 or more. If not, you have a leaky diaphragm, hose or connections.
• Next, either looking from on top, or from under the car (easier to spot under) verify that the actuator moves at least 5/8". If it does, then the actuator itself is working OK. If you have gotten this far, and the actuator does not move at least 1/2" you have either an actuator problem, or sticky vanes, or both. The most common cause is sticky vanes [in the VNT].
• If the actuator is moving smoothly, and the actuator is holding vacuum, then your problem may be in the control circuit (solenoid and forward) or in the turbo. Usually a total actuator failure causes copious white smoke, from unburned fuel, due to lack of boost (and airflow). 
• Completely answering all possible scenarios is beyond the scope of this answer, but I will tell you that commonly there is carbon buildup in the vanes which limits their motion. Mechanical means (disassembly and cleaning) work well, but as you have noted are time consuming. A variant mechanical method, which a friend has done many times, is to move the linkage back and forth vigorously, with the actuator disconnected. This usually results in improved, but not perfect operation. A chemical approach involves a caustic agent, such as spray oven cleaner, being delivered to the turbo, allowing the carbon buildups to soften. Some have used this method, but I have not, although it is tempting.
• Source vacuum off of #10, should be around 27"
• Interesting video of a simple check...not on an ALH, but another VW group diesel, perhaps a Skoda
  

• Solenoid valve vacuum control modules

The valves are mounted on the top of the firewall at the back of the engine compartment, turbo controlling N75 on the right (driver's) side, N18 EGR controlling. in the middle.  The intake manifold changeover/anti-shudder N239 valve is clipped to the intake manifold a bit to the left of center. See here for more information on the N75. If you swap/replace solenoid valves, the hardest part is getting the VW's D-shaped electrical connector to release.  You can hunt around on the TDI club for hints on this, and there are YouTube vids about it. It boils down to inserting a slim flat piece of metal to release the lock, see here.  I used a medical tool from my surgeon father's surgical kit.

Logically I would have done this next, but when I checked the actuator under Further Vacuum Tests, I found it bad. There is info about this in the Diagnosing and Fixing Limp mode for A4 1.9TDI [low power troubleshooting] post

2: Checking out the turbo actuator

• The vacuum actuator (#2 operated by hose #3) should hold vacuum if pumped up with MitiVac
• At idle, that same hose should show 10" according to this: Tee a vacuum gauge in the line going to the actuator. When you start the car you should get about 10 inches of vacuum. The arm on the turbo should also move.When you take off (rev up, drive off?)  the vacuum will drop. (sounds funny). Link
• It ended up that I had a bad, perhaps cracked, actuator diaphragm.  It would work at times, but under hard accel, it would then leak and drop out (vacuum goes to 0 and thus no turbo actuation).  With a vacuum gauge attached while driving to the actuator line, I would see vacuum as I began accel, but then it would drop to nothing as the diaphragm crack opened up.
  

Problem analysis hints and tips

My car has a nylon coupling just for tee-ing in; it's just downstream of the N75 valve on the line to the actuator (that's the lower of the two lines coming off the white top of the N75

Post:

A best starting point would be to get a scan of any fault codes and doing logs of the mass air flow. If your car still has the original MAF sensor it could be the source of your low power issues. The originals were famous for being faulty. To identify it, the VW part number would read 038906461, the latest revision is  038906461C. This requires a VAG.

You can tell if the intake is restricted by taking the large hose off the intake manifold and starting the engine. If it makes a hissing sound it is likely clogged up. It should sound more like thumping on an empty tube (blue man group-like)

Pertinent TDIClub fora threads and posts

Search (Advanced search, VW MKIV-A4 TDIs (VE and PD) only), note that you want ALH engine posts, not BEW

Thread:  Code P0299 "turbo underboost" Resolution Repository Note that this is for Passats

Some pertinent posts:

• Post: The turbo vanes are controlled through the N75 valve, which is basically a solenoid valve. Closed when no voltage is present, open with 12v. When the valve is open, it allows vacuum to pull the turbo vane actuator in, increasing boost. The valve can be tested by trying to pull vacuum though the port labeled "vac". It should hold vacuum and not leak down. You can test the electrical side as well by applying voltage to the valve (negative is the rounded side of the plug, positive is the flat side). It should click and open the path from "vac" to "out". When voltage is removed, the valve should close again. The port labeled "atm" (to airbox) lets the valve vent air quickly when it is cycling. I read on here somewhere that you can use VCDS in basic settings to make the computer cycle the N75 and induce boost. Channel 11 is the number. Click the button at the top and the engine revs to about 1400 and cycles the N75 open and closed causing boost which can be heard and operates the actuator which can be seen. Failed N75 did none of these during the test. Test doesn't indicate pass or fail either, it just operates the system.
  
  
• Can be a clogged cat...also valuable for step by step test layout

Fixing/Replacing the Darn Vacuum actuator

• Preliminaries and tips
• Watch the IDParts video.  It isn't all that helpful as the camera angles/focus are lousy and the turbo is off the car (there are any number of plaintive bitter comments about how this doesn't show how to do it on the car), but it a starting point showing you how things go together, then adjusted/calibrated.
  Pay attention in the video to note:
• The orientation of the heat shield and the actuator vent hole
• the calibration of the actuator: it should start to move the actuator at 3-5" and hit the stop at  15-18"....with 18" being safer/more conservative (boost comes on later), see the video starting at 4:45
  
• If you're changing the actuator on the car, you will need a mechanic's mirror (such as this) to do this calibration.
  
• A MityVac (see the Tools appendix) is necessary for calibrating the stroke of the actuator
  
• Jack the car way up so you can get underneath; do it safely!!
  
  
  
  
  
• Getting to the actuator
  Some people go at this from above (for instance this response on this thread).  I went in from the side and bottom, as follow
  
• Remove the belly pan. 
  Extra  points: Inspect belly pan and what it ties into, the two vertical shields on either side of the engine that run fore and aft.  Odds are there will be various screws and sheet metal 'nuts' and nutserts missing.  Do yourself a big favor.  These parts aren't robust, the screw holes in plastic shields and pans can be torn out if you've ever scraped the bottom of the car...and particularly if you've backed up while doing so.
  Inspect everything and order replacements for what's torn, damaged & missing.  Come winter or mud, these fragile parts protect the engine and are their (not so) strongest when everything is there and firmly fastened together.  See here for replacement shield and belly pan part info
  
• Remove the right front tire.  You should see this, with the vacuum actuator hidden away inside
  
  
  
  
  
  
• Remove the side plastic shield in the passenger side wheel well.  It is held in by two snowflake finger disks pressed over ringed stud attached to the body,  Pry them (and the shield) down off the ringed stud.  It may be easier to remove the side shield after the next step
  
• Undo the rear screw of the plastic air manifold so it can drop down and give you more access to get your hands to the actuator
• hit the two 10mm bolts holding the actuator with penetrator so they'll come undone easily
  
• Tie dental floss to the E or C clip so you can find it when you don't successfully clip it on and it does sprong! and otherwise ends up God knows where.
• You should probably have some extras.  IDparts has a funny looking gennuwine Garrett clip, which are apparently called poodle clips (cuz the ears look like poodle ears), but it doesn't seem to be any easier to install than an e-clip
• The VW tech bulletin on this can be seen here
• Figure out a way to:
• Light the area
• clamp the mirror so you have both hands free to work on the actuator, maybe like this, so you can see the actuator linkage without holding onto the mirror:         
  

        
  More about the nutserts and the belly pan here
  
  
• Taking the old actuator out
  
• is pretty straight forward as you don't much care about the old unit.  A Jonard e-Clip tool may help getting the old e-clip off.  Or you can just whale away until the gosh-darned clip comes off using a long narrow screwdriver or some sort of pick tool
  
• You might want to use the actuator arm length from the old one as a rough guide for the preliminary adjustment on the new unit
  
  
• Putting the new actuator in
•  also straightforward.  Note that the heat shield gets put back on and oriented to cover the air hole.  See the IDParts video.  You will need to gently fit the ball-with-the-hole-in-it over the VNT control pin.  Once you do that, you want to gently wedge something soft but firm (like a small piece of high-density foam) where the green X is below to keep the ball firmly on the VNT control pin (later on the e-clip will permanently secure it)
  
  
• Calibrating the actuator
  
  
  
  
  
• I see some people wing the calibration in various 'clever' ways to get this more or less right.  Folks, doing this correctly and definitively is one of the easiest things about the whole business.  You're going to need a MityVac anyway to diagnose the situation,it's cheap, so do the calibration right: you attach a Mighty Vac to the actuator, pump vacuum while watching the gauge (again, see the IDPart video) and adjust the knurled nut so the actuator arm stroke comes up against the stop at about 18" mercury. That's it: simple and easy and dead-nuts correct. 
  
• One big warning: the actuator arm has a fragile captive ball-with-a-hole-in-it (housed in a sheet metal assembly) that slips over the turbo pin. If you are ham handed you can:
•  wrench that ball out of the arm
  OR
• bend/warp the sheet metal assembly that holds the ball
  AND
• your actuator will be junk.
• Calibrating the actuator's stroke adjustment is done with the knurled nut and then locked in with a nut that spins up the threaded part of the actuator arm to jam against the knurled nut's cage.  Pay attention that you don't ruin the actuator arm.   When you tighten this jam nut, you must also hold the delicate sheet metal assembly that holds the ball-with-a-hole-in-it and the knurled nut so that tightening the jam nut doesn't twist or warp that assembly.  The assembly must remain perpendicular to the turbo pin.  Two things can go wrong if you tighten the jam nut too tight:
1. Unless you hold the sheet metal assembly as you tighten the jam night, it can rotate with the jam nut out of perpendicular with the turbo pin.  The ball-with-a-hole-in-it will allow some deviation, but it should be close to true.
2. You can distort the sheet metal assembly
• What you'll be looking at/for when you pump the MityVac and look for the actuator hitting the stop:
  
  
  
  
  
• Now the worst part: attaching the e-clip
  
  
• This secures the actuator arm with its ball-with-a-hole-in-it over the turbo VNT control pin.
• tie some dental floss on the itty-bitty clip so you can find the sucker when it goes sprong
• Tools are everything.  Here's what I used:
  
  
      


• The Jonard tool is on the extreme right. It can hold an e-clip but when you try and push the e-clip fully into the groove, the e-clip pivots to the side and doesn't snap over.  I also slid a piece of clear vinyl tubing over the tool so I could easily rotate/spin it to get alignment with the shaft recess where the e-clip goes...the tool is flat and otherwise wants to be held flat between your thumb and finger....which may not be the right axis rotation angle to meet the pin groove.
  
• In the middle are surgical scissors used to trim off the floss after the clip was in the groove,
• On the left is a blunt nosed, strong locking hemostat from my father's surgical tools that gripped the e-clip (strongly enough that it didn't pivot while being pushed into the groove) and then locked down (so you don't have to hold it closed, effectively surgical Vise-Grips that can fit into the tiny space where the e-clip goes).  But it has to be a strong blunt nosed locking hemostat to hold the e-clip firmly.  One such from Amazon here; you do NOT want the delicate needle-nosed sort
  
• I got a pair of 1/4" regular e-clips from the Hillman fasteners drawer aisle at Tractor supply, 99¢ for two.  From IDParts, I got two Garrett 'poodle' e-clips, which is what I ended up getting on the VNT control pin's retaining groove.  The poodle clip can be seen in the left hand picture loose but tied with floss.
  
• I  spent 6 hours over 3 days fighting with this ...I have to look through a mirror which reverses my motion.  I couple of times I have gotten the clip to where I think the clip should go but have been unable to even begin to shove the clip into the recessed slot.  Everything had to be right: the lighting, the mirror position, the actuator arm fully over the VNT control pin so the groove in the pin is exposed, the e-clip coming in straight at the groove and properly aligned.  Then <snick> and the blessed thing is done.
  
• McMaster has what looks like single size and more expensive clip installation tools, even specialized ones for poodle clips
  
  
  
  TDIClub needs a tool rental library, :).
• When you finally get it in place, it will look like this seen from the bottom (taken with a telephoto macro lens..would that it were that big and could be reached directly).  Note that a little bit of the floss is still attached.
  
  
  
  
  
  
• Good luck.....
  

Considerations

• One person pointed out that, if you had a perforated or corroding actuator diaphragm, crap would be sucked into the vacuum system, clogging and obstructing the control valve/modules and check valves.  So a failing actuator could screw up other parts of the vacuum system!
  

• Running vacuum line through firewall (for gauges)
• Post: The rubber grommet looks like a little snowman (large on bottom to a smaller rounded top), look down by the brake booster and you'll see it. You may have to pry back some sound insulation to get at it under by the driver's foot area, to the side of the steering column (right by the u-joint and the rubber boot that protects it).
• Post (installing the tubing for a boost valve): To breach the firewall I chose a spot above and to the left of the brake pedal where a major bundle of wire enters. This area may be difficult to reach without removing the trim panel above the pedals. This will require moving the 2 lower dash trim panels then the panel over the pedal area.(damn tidy Germans) To feed the tubing I took a coat hanger bent it back about an inch on itself and slipped the tubing over this. I then taped it up with electrical tape and poked it through the firewall to the side of the wire bundle. From the engine bay you can pull the tubing through taking care to make sure it does not bind/crimp on the interior side.

Background Information

Parts in the Vacuum System Controlling Turbo Actuation 

 ALH stock Vacuum System Diagram (at right) Legend

Matching part numbers:

1: N239 - 1K0906283A, 7.02256.00.0 (2000 on, D shaped connector), 1J0906283A (Before 2000, square connector)
4: N18 - 1J0906627, 7.02183.01.0
6: N75 - 1J0906627A, 7.02184.01.0*
7: 046905291A
10: Part of  Vacuum Pump to Brake Booster Line  1J0612041GD, See 2nd image below right
11: Vacuum pump, 038145101B, 7.24808.05.0;
13: 045131501C

TDI Club Forum post
Q: "Are N75 and N18 'exact' same, they have identical part numbers apart from letter A at end off N75 number, and they look identical with exact hose connections and power plug!!!
A: They look very similar and work the same way. But the N75 controls the turbo VNT actuator and the N18 controls the EGR."
Notes:

• N18 has a black top, N75 has a white top.
• "You can swap the N75 and the N18 for testing."
• The two ports on the white top of the N75 open into the same chamber, the port on the black bottom goes to the turbo actuator
  
• There are two interchangeable types of (white top) N75s

• The original is the 1J0906627A, 7.02184.01.0, which has the black port facing the other direction from the white ports on the top (as shown in the diagram to the right)
• It is functionally interchangeable with the  1K0906627A,
   7.00868.02.0 which has all three ports facing to the right. This N75 was used with the followon BEW engine, late 2005/6, but can be used with the ALH
  

Vacuum Hose

ID Parts, Vacuum Hose Kit

McMasters Carr silicone vacuum hoses

Ft. 5041K521 Metric Silicone Rubber Tubing Firm, 3 mm Id, 8 mm O.D., 2.5 mm Wall, Black (Same as 5041K52)
Ft. 5054K531 Metric Silicone Rubber Tubing Soft, 4 mm Id, 8 mm O.D., 2 mm Wall, Black (Same as 5054K53)
A4 B/G/J ALH:
10 foot of black 3 mm.
5 foot black 4mm

I'd say add a foot to each, just barely squeaked it out.  You can also get silicone tubing from China inexpensively in different colors; search on EBay for '4mm silicone vacuum tubing'.

Parts Offerings/Sourcing,

• Limp Mode Fix Kit (A4 ALH)
  
  
• Vacuum System Parts
  
  
• Vacuum Pump to Brake Booster Line (A4 ALH)
  
  
• EGR Valve (A4 ALH). Not a solenoid vacuum valve, but an actuator allowing exhaust gas recirculation.
  
  
• Vacuum Pump: $225 for Pierburg from IDParts, $55 from Ebay/HongKong
  

• Shields & Belly Pan parts, listed for manual tranny
  

• Passenger side engine side shield, VW1228103,1J082525, $20-$30 from Ebay,
• Driver side ditto, VW1228111 1J0825250K (I think)
  
• Replacement belly pan, original plastic or aluminum upgrade available from IDParts and ECS Tuning. Part number for original plastic one are, IIRC, 1J0825237M, VW1228106
  
• Snowflake retaining discs that go over ringed studs to secure the side shield to the frame, part # n903-350-04
• IDParts has a complete set of all the belly pan fasteners, which includes:
  
• Torx belly pan retaining screws part #N90775001 (quantity: 10)
  
• Rectangular nutserts for the rear of belly pan (go into rectangular holes in the cross member), part #N10327102, $1.40 the pair
• Push on sheet metal 'nuts' are commonly available from any good hardware store with those pull out drawers of specialty fasteners (quantity: 8)
  
  
• Fender liner information (to protect the intercooler) is here
  

Nomenclature

• VNT: Variable nozzle turbine pressure control (as opposed to simple waste gate). There are vanes that change how much power is derived from the exhaust gases and how fast the turbo spins.  Picture here
  

Tools

• I have a Scan Gauge2 with which I can monitor much of the computer data including scan codes.  In daily use, I watch my MPG. Note the SCII includes the MAP parameter, manifold absolute pressure, which is the boost pressure PLUS the normal pressure (15 PSI at sea level).  So if the MAP parm is 30, that's an actual boost pressure (at sea level) of about 15 PSI.  When the turbo is boosting things, like at idle, the MAP will be, natch, around 14-15.
  
• A MityVac MV8500 for doing vacuum testing, used both to gauge vacuum and to pump down to manually operate actuators. The plastic one (which is good enough) is $40 used on Ebay, $50 new from Amazon
• You'll need a good mechanic's mirror on a flexible stalk to see the actuator linkage
  
• The Jonard e-clip tool might be helpful.  It has one end to remove e-clips, the other to install (but not very well)
• A strong substantial locking hemostat worked best for installing the e-clip
  
• VAG which gets into serious engine diagnosis, see here.  I was able to do everything I needed to do without one
  

Parts Sources

• Ebay.  Don't buy cheap junk.  Buy Pierburg or OEM VW
• McMasters - Carr (vacuum hose) also e and poodle clip installation tools
  
• ID Parts  They specialize in VW TDI parts, including upgrades and hard to find items
  
• ECS Tuning