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FOREWORD. |
THE TOOLS. |
The following outlines the procedure for
removing and cleaning the drive-by-wire (DBW)
throttle body (officially known as the throttle
valve control module) on a MKIV VW. The
procedures were based on a 99.5 Jetta GLS VR6
and may be different on MKIV cars with different
engines (1.8T, 2.0), body styles (Golf, GTI, New
Beetle) and from different model years.
Specifically, the procedures for removing and
reinstalling the throttle body (herein referred
to as TB) may differ due to slight differences
in the design and orientation of the TB,
however, the general removal/reinstallation
procedures, as well as the cleaning procedures
should be very similar. Please do these
procedures at your own risk and be ready to make
small adjustments while doing them. Also, please
be observant while removing parts so that they
go back together correctly.
Before proceeding any further, I must make it
clear that the DBW TBs used on the MKIV vehicles
are high-precision, electro-mechanical devices.
If you damage the servos and sensors which
control the motion and position of the throttle
valve (also known as the butterfly valve) while
performing this procedure, there is a very great
chance that your engine will not run correctly
and the TB will need to be replaced. Since a new
TB costs around $500, this is something that you
will obviously want to prevent from happening.
Therefore, be extremely careful when performing
the procedure and heed the warnings and cautions
that are given. I am not, nor will be held
responsible if you mess up your TB while doing
this procedure.
This DIY is broken up into three parts...
PART I: Deals with the removal of the TB
from the intake circuit. Two methods for
removing the TB are given. The first method is
the "quick and dirty" method and requires that
the least number of things be
disconnected/removed in order to disconnect the
TB. I did not perform this procedure, so I have
no idea how long it takes. Nevertheless, I have
supplied it for all the minimalist DIYers out
there who like to keep things simple. (Note: If
you follow this method, you may notice that the
pictures posted for this method do not actually
show anything disconnected. Please disregard
these inconsistencies. Since I did not perform
this procedure, I did not have the appropriate
pictures and used those taken after everything
was already reassembled. Just follow the written
directions, using the photos only as a
reference, and you should have no problems.) The
second method is the "slow and thorough" method
and requires that significantly more things be
disconnected. The advantages of this method are
that it (1) allows various other parts of the
intake system, such as the main intake tube and
PCV circuit to be examined and cleaned and (2)
unclutters the "workspace", making it
significantly easier to remove the coolant lines
from the TB. This method is the one that I
followed when cleaning my TB and I recommend
that others use it as well. If you're familiar
with this area of the engine bay, it will take
approximately 30-60 mins to remove the TB using
this method.
Part II: Deals with the cleaning of the
TB. The cleaning procedure should take 30-60
mins or more, depending greatly on how dirty
your TB is and how careful and thorough you are
when cleaning it.
Part III: Deals with the adaptation of
the TB to the engine control module (ECM) using
a VAG-COM or other suitable scan tool. It is not
absolutely necessary to perform this procedure,
however doing so immediately following the
reinstallation of the TB will help insure the
smooth operation of the engine when it's first
started. |
The tools/parts needed to perform the procedures
are:
1) 10mm wrench or socket (to disconnect negative
battery lead)
2) Appropriate tool for removing hose clamps. If
you have the stock spring clamps, a pair of
channel lock pliers works great for this purpose
since the jaws are roughly perpendicular to each
other (helps prevent clamps from slipping in
plier jaws) and the jaw width can be adjusted
for each particular clamp size. If you have
screw-type clamps, you'll need the appropriate
screwdriver.
3) 5mm hex/Allen wrench (to remove TB from
intake manifold)
4) Phillips screwdriver (only needed in "slow
and thorough" method if removing MAF housing
from air filter housing)
5) Flat blade screwdriver (to help remove spark
plug wire boots from coilpack - not needed for
"quick and dirty" method)
6) T30 Torx driver (to remove engine cover
pieces - not needed for "quick and dirty"
method)
7) Can of intake/TB cleaner
8) Q-tips or something similar (to gently scrub
away the TB deposits)
9) Sheet of plain white paper
10) Paper towels or rags
Optional...
11) New TB-to-manifold gasket. The Bentley
manual instructs that this gasket should be
replaced when the TB is removed, but more than
likely it can be reused. Mine was still in
excellent shape so I reused it. If you are
uncomfortable doing this, purchase a new gasket.
12) VAG-COM or other suitable scan tool (for
performing adaptation of TB to ECM).
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PART I: REMOVING THROTTLE
BODY. |
STEP 2. |
The TB is located at the back of the engine bay
between the air intake hose and the intake
manifold and is indicated by the yellow arrow in
picture above. |
The TB is shaded blue in the picture above.
TWO OPTIONS HERE:
- To follow the "quick and dirty" removal
method, follow steps 3 through 11.
- To follow the "slow and thorough" removal
method, follow steps 12 through 30. |
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STEP 3 - QUICK AND DIRTY
REMOVAL METHOD. |
STEP 4. |
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Remove the battery box cover and disconnect the
negative (-) battery lead from the battery using
a 10mm wrench or socket. Secure the lead away
from the (-) battery post so that it does not
accidentally touch it while you're working on
the car. |
Disconnect the harness connector from the TB.
The connector is indicated by the yellow arrow
in the picture above. |
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STEP 5. |
STEP 6. |
Unclip the coolant hose (red arrow in picture
above) and the PCV vacuum-assist hose (yellow
arrow in picture above) from the top of the air
intake tube. |
Disconnect the upper coolant hose (yellow
arrow in picture above) and lower coolant hose
(blue arrow in picture above) from the TB. To do
this, use the appropriate tool (pliers or
screwdriver) to release the tension from the
hose clamp, slide the clamp down the hose and
out of the way (for spring clamps, make sure the
clamp is moved past the end of the nipple inside
the hose or the clamp will reapply pressure to
the nipple when released), and then pull the
hose off of it's nipple. |
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STEP 7. |
STEP 8. |
Release the tension from the clamp securing the
main air intake tube to the TB (indicated by
yellow arrow in picture above) and then slide
the intake tube off of the TB. |
Using a 5mm hex/Allen wrench, remove the 4 long
bolts that secure the TB to the intake manifold.
There is one bolt at each corner of the TB, two
of which are indicated by the yellow arrows in
the picture above. Support the weight of the TB
as you remove the last bolt. You wouldn't want
the TB to fall - it is a delicate,
high-precision device. Note that one of the
bolts also secures a ground wire to the TB
(indicated by red arrow in picture above). In my
case, the ground wire was secured by the lower,
front bolt, but a different bolt may be used in
your car. Remember which bolt the wire was
attached with so that it can be reinstalled in
the same position. |
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STEP 9. |
STEP 10. |
While holding the main
intake tube and coolant/vacuum hoses out of the
way, pull the TB up and off of the intake
manifold.
CAUTION: Be careful not to let ANYTHING fall
into the intake manifold while the TB is
removed. You don't want any foreign objects
being sucked into the engine when it's first
started - this may cause severe damage!
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The yellow arrow in the picture above indicates
the gasket that seals the rear of the TB to the
intake manifold. Prior to reinstalling the TB
(new or existing), either replace the gasket
with a new one or decide to reuse the existing
one. If you decide to reuse the existing gasket,
make sure to clean it by wiping it with a rag or
paper towel to remove any debris or contaminants
that may be on the mating surface. (The red
arrow in the picture above shows a better view
of the ground connection that is secured to the
TB by one of its mounting bolts.) |
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STEP 11. |
STEP 12 - SLOW AND
THOROUGH REMOVAL METHOD. |
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If you are replacing the TB, install the new
unit by following steps 3 through 9 in reverse
and then proceed to Part III (TB adaptation). If
you are cleaning your existing TB, proceed to
Part II. |
Remove the battery box cover and disconnect the
negative (-) battery lead from the battery using
a 10mm wrench or socket. Secure the lead away
from the (-) battery post so that it does not
accidentally touch it while you're working on
the car.
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STEP 13. |
STEP 14. |
Release the tension from the clamp securing the
main air intake tube to the MAF housing
(indicated by yellow arrow in picture above) and
then slide the intake tube off of the housing.
If you're like me and are paranoid that anything
you do under the hood can potentially harm the
poorly-designed MKIV MAFs, you may also want to
remove the MAF and put it in a safe place. It is
not necessary to do this in order to remove the
TB, but you never know with these MAFs. If you
want to remove the MAF housing from the air
filter box, disconnect the MAF harness connector
(red arrow in picture above), remove the two
Phillips screws that secure the MAF housing to
the air filter box (one of the screws is
indicated by the blue arrow) and GENTLY slide
the housing out of the filter box. There is a
large gasket sealing the two which snaps into
the opening in the filter box, so it may require
some force to separate them. |
Carefully remove the spark plug wires from the
ignition coilpack by pulling the rubber wire
boots off of the posts on the coilpack, as shown
in the picture above. This may be difficult due
to the suction created by the seal between the
boots and posts. I used a flat blade screw
driver to carefully slide the boots off of the
posts. (Be careful not to rip the boots if you
do this or the engine may misfire when moisture
is present.) I recommend that you mark each wire
so that it is reinstalled on the correct post
later on. |
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STEP 15. |
STEP 16. |
Unclip the spark plug wires from the channels in
the engine cover, as shown above. |
Remove the small engine cover piece with the VW
logo on it by removing the single T30 Torx
screw, indicated by the yellow arrow in the
picture above. |
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STEP 17. |
STEP 18. |
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Remove the long, thin
engine cover piece on the passenger's side of
the engine by removing the two (2) T30 Torx
screws indicated by the yellow arrows in the
picture above. |
Remove the main engine cover piece by removing
the four (4) T30 Torx screws indicated by the
yellow arrows in the picture above. As you lift
up on the cover piece, you will need to thread
the spark plug wires through their respective
holes in the cover in order to fully remove it. |
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STEP 19. |
STEP 20. |
The picture above shows how the top of the
engine should look with the three engine cover
pieces removed. |
Disconnect the electrical harness connectors for
the TB (yellow arrow in picture above) and PCV
valve heater (red arrow in picture above). Next,
unclip the TB harness connector lead from the
top of the coolant hose which passes over top of
the main air intake tube (white arrow in the
picture above) and move the lead out of the way.
Finally, disconnect the vacuum-assist hose
(green arrow in picture above) from the PCV
valve S-hose (between valve cover and main
intake tube), unclip the hose from the top of
the main intake tube (blue arrow in picture
above) and move the hose out of the way. |
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STEP 21. |
STEP 22. |
Disconnect the PCV S-hose from the PCV valve on
the main intake tube by pushing the two serrated
tabs together (yellow arrows in picture above)
and carefully pulling the hose off. If you want
to also clean the inside of the PCV S-hose
(there WILL be oil in it), release the tension
from the clamp on the other end of the S-hose
(red arrow in picture above), slide the clamp up
the hose a bit and then pull the hose off of its
nipple. (Note the position of the bend in the
S-hose relative to the bolt/nut just to the rear
of the oil cap. There should be sufficient room
between the hose and bolt so that the bolt does
not cut into the hose. There is a depression on
the underside of the hose at the bend to provide
more clearance. Make sure to reinstall the hose
in the same position later on so that abrasion
does not occur.) |
The picture above shows the inside of the PCV
valve/heater on the main intake tube. If you
look closely, you can see the abundance of
condensed oil vapors. |
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STEP 23. |
STEP 24. |
Disconnect the upper
coolant hose (yellow arrow in picture above)
from the TB. The nipple on the TB is
approximately 1" long, so the clamp has to be
moved up the hose at least that much in order to
remove the hose from the nipple. |
Disconnect the lower coolant hose (yellow arrow
in picture above) from the TB. Again the nipple
on the TB is approximately 1" long, so the clamp
has to be moved down the hose at least that much
in order to remove the hose from the nipple. |
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STEP 25. |
STEP 26. |
Disconnect the vertical coolant hose (yellow
arrow in picture above) from the T-junction in
front of the TB/main air intake tube. Next,
unclip the horizontal portion of the coolant
hose T-junction from the top of the main intake
tube (red arrow in picture above) and then move
the hose out of the way. At this point, there
should be no coolant hoses attached to the TB,
nor should there be any coolant hoses or
electrical leads passing over the top of the
main intake tube. |
Release the tension from the clamp securing the
main intake tube to the TB (indicated by yellow
arrow in picture above) and then slide the
intake tube off of the TB. |
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STEP 27. |
STEP 28. |
The picture above shows
the large amount of condensed oil vapor in the
main intake tube due to the PCV circuit. I wiped
this oil off the inside of the tube with a paper
towel. (I can only imagine how much oil is in
the intake manifold and elsewhere in the engine.
Someday I'll clean it all out.) |
Using a 5mm hex/Allen
wrench, remove the 4 long bolts that secure the
TB to the intake manifold. There is one bolt at
each corner of the TB, as indicated by the
yellow arrows in the picture above. Support the
weight of the TB as you remove the last bolt.
You wouldn't want the TB to fall - it is a
delicate, high-precision device. Note that one
of the bolts also secures a ground wire to the
TB (indicated by red arrow in picture above). In
my case, the ground wire was secured by the
lower, front bolt, but a different bolt may be
used in your car. Remember which bolt the wire
was attached with so that it can be reinstalled
in the same position.
CAUTION: Be careful not to let ANYTHING fall
into the intake manifold while the TB is
removed. You don't want any foreign objects
being sucked into the engine when it's first
started - this may cause severe damage!
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STEP 29. |
STEP 30. |
The yellow arrow in the
picture above indicates the gasket that seals
the rear of the TB to the intake manifold. Prior
to reinstalling the TB (new or existing), either
replace the gasket with a new one or decide to
reuse the existing one. If you decide to reuse
the existing gasket, make sure to clean it by
wiping it with a rag or paper towel to remove
any debris or contaminants that may be on the
mating surface. I determined that the gasket in
my car was in good enough shape to be reused, so
that's what I did. No biggie. (The red arrow in
the picture above shows a better view of the
ground connection that is secured to the TB by
one of its mounting bolts.) |
If you are replacing the
TB, install the new unit by following steps 12
through 28 in reverse and then proceed to Part
III (TB adaptation). If you are cleaning your
existing TB, proceed directly to Part II. |
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PART II: CLEANING THE
THROTTLE BODY. |
STEP 2. |
The four pictures
above show different views of the inside of the
throttle body. The yellow arrows in these
pictures point to the oil, gum, varnish and
other crap that deposits itself inside the TB
over time. In my case, most of the deposits were
located between the edge of the throttle valve
and the TB wall (valve at idle position or fully
closed) and on the roof of the TB wall behind
the throttle valve. |
To insure the proper operation of the TB, it is
imperative that the deposits in the pictures be
removed. IMO, the most critical of these
deposits are those which lie between the edge of
the throttle valve and the TB wall. Normally
there is a small 1-2mm gap between the edge of
the valve and the wall. At idle, the valve
remains fully closed and the air passing through
this gap allows the engine to idle smoothly. As
deposits build up in this gap, the amount of air
that can pass through decreases and the ECM/DBW
system must compensate by resetting the idle
position of the valve from fully closed to open
a few degrees or so. Naturally, as the amount of
deposits increases, an increasing larger
compensation must be made by the ECM. At some
point, the ECM cannot compensate by opening up
the valve any further and the following OBDII
code is commonly stored:
17990 - Idle Adaptation Limit Reached
P1582 - 35-00 - -
Cleaning the TB often gets rid of the code,
since it allows the throttle valve to be fully
closed at idle, i.e., no idle adaptation is
needed.
NOTE: The above description is MY
understanding of how the TB operates at idle. If
this is incorrect, please inform me and I will
change/remove the description. |
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STEP 3. |
STEP 4. |
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In order to safely clean the inside of the
TB, you will need a can of intake/TB cleaner
(the stuff I used is shown in the picture above
- make sure to choose something that is
relatively gentle and will not harm DBW TBs -
some carb-type cleaners are not), something to
gently scrub off the deposits on the throttle
valve and on the TB wall (I used Q-tips and
paper towels) and a sheet of ordinary white
paper |
Cut the paper into thin, triangular pieces
approximately 1" x 4" (size is not critical), as
shown in the picture above. Also shown are some
EXTREMELY dirty Q-tips that had already gone at
the deposits in the TB by the time I took this
picture |
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STEP 5. |
STEP 6. |
To clean the TB, spray the TB cleaner onto the
deposits inside the TB, allow it to soak in for
a few seconds and then gently scrub away the
deposits with the Q-tips and/or paper towels.
Using this method, you should be able to remove
all of the deposits EXCEPT for those between the
edge of the throttle valve and TB wall. We'll
get to those deposits shortly. First, here are
some VERY important warnings.
WARNING: When spraying the TB cleaner inside
the TB, I HIGHLY recommend that you hold the TB
with the electronic control module portion of
the TB ABOVE the body of the TB. Orienting the
TB in this manner while cleaning it will help
prevent the cleaner from leaking past the seals
between the TB body and control module and
possibly damaging it. While the seals should be
a sufficient barrier to this happening, why take
the chance with a $500 piece of equipment.
WARNING: Be careful not to press too hard
against the throttle valve while cleaning it.
Unlike a drive-by-cable (DBC) TB in which the
throttle valve is allowed to move freely and is
held closed by a spring, the position of the
throttle valve in a DBW TB is controlled
electrically, most likely by a high-precision
stepper motor. Because of this, the throttle
valve will not move freely and can be easily
damaged if forced to move against the resistance
of the stepper motor. This does not mean that
you cannot apply a small amount of pressure to
the throttle valve with the Q-tip when cleaning
it. Just be careful not to use too much
pressure. When in doubt, use the least amount of
pressure needed to remove the deposits and you
should be OK. |
Since the throttle valve will not move freely
due to stepper motor used by the DBW throttle
valve controller, you cannot simply move the
throttle valve out of the way to remove the
deposits that collect between the edge of the
throttle valve and the TB wall. Instead, I
recommend that you use to the small strips of
paper to clean this area. Spray a little TB
cleaner into the gap between the edge of the
throttle valve and the TB wall and use the
corner of one of the strips of paper to
carefully scrape the deposits out of the gap.
Once the deposits have been removed from a small
area of the gap, slide the paper into the gap
completely and move it back and forth to scrape
the deposits out of the gap, similar to using
dental floss to remove food from between your
teeth. Spray additional cleaner into the gap as
needed during this procedure. Using this method,
it should be possible to remove virtually all of
the deposits from the gap. Most likely, the gap
near the axle for the throttle valve will be too
narrow to get the paper into it, so there may be
a very small amount of deposit left remaining in
the gap near the axle. This is not a big deal. |
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STEP 7. |
STEP 8. |
The picture above show
how the gap between the edge of the throttle
valve (in the fully closed position) and the TB
wall should look once the deposits are removed
from it. |
The pictures above
show various views of the TB following the
cleaning procedure. No big surprise that it
looks much better than it did prior to the
cleaning. |
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STEP 9. |
STEP 10. |
The pictures above of paper towels and Q-tips
used during the cleaning procedure illustrate
that while the TB did not look that dirty, quite
a bit of deposits were removed during the
cleaning process.
WARNING: Prior to reinstalling the TB, make
sure to let it dry thoroughly or damage to the
electronic control module or throttle position
sensors may result. To speed up the process, I
inserted clean strips of paper into the gap
between the edge of the throttle valve and TB
wall to remove the cleaner held in there by
capillary forces. Following this, I allowed to
the TB to sit for approximately 30 mins before
reinstalling it. I recommend that you wait this
long or more before reinstalling your TB. |
The picture above shows
the cleaned TB ready to be reinstalled. |
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STEP 11. |
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To reinstall the TB, follow the steps for the
removal method in Part I that you used in
reverse, and then proceed to Part III.
VW TECH BY: Gary Thompson
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