Engine Problems and Diagnostics
The first thing to do if you're having engine problems is to dump the
fault codes from the computer. It's easy to do with a homemade
1115 LED test light. For more info, go to the Diagnostic
Fault Codes page.
Symptoms: Idle will constantly bounce between 1600 and 400 RPM,
stalling. This is a very common problem with these cars.
Idle Stabilizer Valve (ISV)
typically cause problems because of either a bad electrical connection
or some kind of internal gunky build-up.
If cleaning the ISV and it's electrical connections don't fix your idle
problems, look for vacuum leaks (like the idle screw hole, there is an
O ring that might have decomposed) and check out your idle
switch before you replace the ISV. A new ISV is expensive. If you
faced with replacing your ISV, please note that there are two
Locate the ISV. On the early 1990 cars, it's on the side of the airbox.
It has two rubber vacuum hoses attached and one electrical connector. I
have colored the diagram of the passenger side of the engine
to the right (ain't I sweet?). In the picture, the ISV is colored
the rubber hoses are blue and the electrical connection is red. The
'90 and all '91 cars have a slightly different arrangement with the ISV
mounted on the boot between the throttle body and the airbox.
A quick test to see of the ISV is causing the problem is to unplug the
electrical connector while the problem is occurring. If the idle is now
steady (higher or lower speed is normal), then the ISV is the likely
Check the contacts on the electrical connector. If they are wet,
or loose, clean them up with contact cleaner (available at car stereo
or Radio Shack) and reconnect securely. If you're lucky, this will cure
If problem persists, remove ISV by loosening the two hose clamps and
the hoses, then unscrew the ISV from the plastic airbox lid.
THOROUGHLY spray carb cleaner into the two hose connections on the ISV
and allow to soak inside the unit, then pour it out. Repeat this
several more times until the stuff you pour out looks clean. Better
fill a small container with carb cleaner and let the ISV soak in it for
an hour or two, then spray it a few more times. When you think you've
it enough, clean it some more!
If you have an early '90 car with the Hitachi ISV (pictured at left
then you can try a more thorough cleaning procedure:
To disassemble, remove (cut off and discard) the crimped-on sheet metal
anti-tamper end cover.
Before unscrewing the brass end plug, mark its position relative to the
housing so it can be replaced to the same position, thus maintaining
same spring tension on the valves.
Disassemble the unit completely and clean all parts with solvent.
Lube the two shuttle bearings with a drop of silicone oil on each.
Reassemble the unit making sure the brass end plug is returned to it's
Reinstall valve on air box and insure no air leaks at the hose
Adjust idle speed as described below.
Reattach the ISV and hopefully the problem is gone, because a new ISV
Cold Start/Idle Problems
Early 1990 cars (CQ VIN <= 13610) have the Hitachi unit shown on the
left -- Audi P/N 034 133 455 A
Later 1990 cars (CQ VIN > 13610) and all 1991 cars have the Bosch
shown on the right -- Audi P/N 034 133 455 B
Symptoms: After a cold start, the car stalls or threatens to. Also,
somewhat erratic idle.
Check the rubber connector from the filter housing/air sensor to the
throttle manifold for cracks that would allow unmeasured air to enter.
(approx. $50) Also check for any other sources of vacuum leaks.
Unofficial Idle Adjustment (may only work on pre-March '90 cars)
(Bernie Benz) This procedure sets the idle speed to minimize the
of sudden engine braking when the throttle is slammed shut.
Official Idle Adjustment
With engine at operating temperature, disconnect the ISV
Adjust the idle speed with the throttle valve air bypass adjustment
to 700 to 750 RPM. (This is just below the speed at which the ECU
will control idle.) This sets a minimum idle speed well above zero.
Reconnect the ISV elec. connector, and check the idle speed. The
should control idle at 800 to 900 RPM. If it's faster, the ISV is not
following computer control, the sign of a sticky valve.
Warning: Bentley says the idle and CO content are interrelated, and
must be adjusted together. The following procedures may be good for
adjustment; however, they may cause more problems than they fix.
Pre March 1990 production date
Post March 1990 production date
Clamp crankcase ventilation hose behind fuel pressure regulator, then
oil dipstick and cover tube with a lint-free rag to prevent oil spray.
(This step is probably more important for the CO adjustment rather than
idle adjustment, so can probably be skipped.)
Under driver's side glove/map compartment (near steering column) you
find two diagnostic connectors, with two jacks on each one.
the lower jack between each connector (A1 and B1).
Start car, turn off all accessories, make sure car is warm but radiator
fan is not running, check idle speed. Should be 800 RPM +/ 50
Adjust idle speed to spec at adjusting screw on throttle
body (accel.cable is sticking out of it, adj. screw is pointing
the air cleaner).
Crankcase Breather Hose
Remove rear electrical connector from carbon canister shutoff valve.
With engine idling and all accessories off, install spare fuse in the
of the fuel pump relay.
Adjust idle speed to spec at adjusting screw on throttle
body (accel.cable is sticking out of it, adj. screw is pointing
the air cleaner).
These cars (the early ones, at least) came with a rubber crankcase
breather hose. The hose comes out of the lower engine block on the
side, then runs toward the firewall a few inches, then turns to the
side to enter a metal tube. In time, the hose becomes very soft and
and may collapse or rupture. The replacement is a metal tube with two
lengths of rubber hose clamped to each end. The P/N for the metal tube
is 054 103 227 A, but make sure you ask for the kit that has all the
pieces with it. Replacement is straightforward, but frustrating because
of limited access and the rigidity of the metal replacement compared to
the original rubber hose.
For easier access to the lower clamp, unbolt the metal support wire
holds the two hydraulic hoses that run from the pump toward the
Look just below/behind distributor, to the back of the engine (a light
helps here), and you'll see where a long metal breather tube (runs
across engine bay and behind engine) connects to the rubber breather
To disconnect the two, first loosen the mounting bolt that holds the
tube behind the engine block. This will allow you to maneuver that tube
(helpful during reassembly, too). A medium sized screwdriver will get
there, from the top. If you still have difficulty getting to the clamp,
consider removing the battery for easier access
The bottom of the hose mounts on the driver's side of the block, just
the bracket that holds the plugs for the 02 sensor. Loosen the hose
Take note of the placement of the hose--you'll need to re-route the new
one in the same place.
The hose will probably be in such horrible shape that when you pull it
off the lower mount it will break apart, causing a bunch of debris to
into the crankcase. To avoid this, be very careful as you remove it.
The new hose is metal, with two rubber ends. The hoses are tight enough
so that they fit over the metal piece without the need for clamps, and
Audi doesn't provide any for this purpose. Use the old clamps just to
the hose ends down over the mounts, not onto the metal replacement. For
extra security you can buy a medium and a small sized hose clamp to
the rubber ends onto the metal center section.
Replacement is opposite of removal. Getting everything lined up can be
difficult, so be patient. You can connect either end first, depending
which way you find to be easier.
The first thing to do is check the fault codes. They should point you
in the right direction. If they don't, or you need a quick fix on the
there are some things to check. A fairly common cause of this is
just a poor connection on the fuel pressure regulator, or the ground
that comes out of that connector and attaches (usually) to the air
on the intake manifold. The 20V is completely timed by the computer, so
distributor placement doesn't have to be too exact. There is a big
connector that is a few inches in front of the distributor cap towards
the front of the engine, this is the multipoint connector that has the
O2 sensor, distributor controls, engine management etc on it. If that
half off or corroded/wet the car will act funny. Try taking that
apart, cleaning it, and putting it back together. You might want to put
in some anti-corrosion spray in there too.
(Phil Payne) Here are some general rules of thumb that apply to any
|White smoke, acrid smell
||Probably from head gasket leak (usually fails at back of an
-- replace head gasket (duh!)
|Blue smoke on shifting, burnt oil smell
||Valve stem oil seals
||Find the right mechanic, and it's a surprisingly cheap job
|Blue smoke on overrun w/o shifting, vaporised oil smell
||More serious wear, perhaps rings
||Very rare in Audis, common in Beemers
|Grey or black smoke, just plain stinks
||Seriously rich mixture
||Adjust mixture (duh!)
Erratic Coolant Temperature
Symptoms: Coolant temperature gauge is erratic or non-functional;
no heat from the climate control.
There are two possibilites. The first thing to check is the thermostat,
because it's easier and cheaper. If that's not the problem, you may
to replace the multi-function temperature switch per instructions
Follow upper radiator hose to housing attached to block. On lower part
of this housing there is a multi-function sensor with a rubber boot
4 or 5 wires sticking out , and a bronze or copper colored hexagonal
It is threaded to housing (normal thread direction).
With engine cold or lukewarm: Run a small screwdriver carefully around
the perimeter of the boot, between the boot and the sender body. The
is to separate any stickiness. Push down the boot from the upper edge
work it down. (Do not pull down the wires).
There is a plug in connector inside with 3 or 4 contacts. The boot
down will disconnect the plug.
Prepare the replacement part next to you so that you don't have to walk
away. Place absorbent towel or rag underneath the sender.
Using an open end wrench loosen sender and finish extraction by hand
maintaining slight upward pressure to avoid excessive coolant loss.
When sender completely loose, pull it out and plug opening with left
index finger. Make sure you have the flat washer on the sensor you
If it lodged into the hole, pry it out. The new one will leak with two
With right hand (quickly without panic) insert new sender and initiate
thread. Do not over-tighten with wrench (brass threads).
Reconnect plug redress boot and clean the coolant from the block etc.
you broke the tabs, don't worry, just about every replaced sensor has
Warm up engine check for leaks and enjoy your new temp reading and ECU
If you need to replace the fan, consider getting a 6-blade VW part
(P/N 811 119 113 B) for about $60. It's a bit noisier than the stock
but pulls more air. It does not come with new screws and bolts, so
lose the originals. When removing the old fan, note that on the lower
side of the fan at the very bottom of the fan shroud there is some
wiring that feeds down to the sensor at the bottom right of the
Do your best not to pinch this wire and make sure on install of the new
fan that you have not pulled it up so that there is not enough slack to
reconnect it to the sensor. You will probably need to cut a tie wrap
is holding that wire in place in order to get at the bottom nut.
the following two wiring updates while you're in there.
The wiring harness to the fans on these cars appears to be a bit short.
Mechanical and thermal stresses may cause a failure at the wiring
To fix or prevent the problem, splice in some extra wire to provide
relief. At the same time, you should add in a fuse to the ground wire
In later cars, Audi put an 80 amp fusable link into the ground wiring
for the radiator fan. This setup is used to avoid sending 80+ amps of
to the fan ground if the fan bearings freeze up . This could possibly
an electrical fire, or at a minimum it will fry your electrical
Here are the Audi P/Ns for retrofitting a ground fuse to the fan
Or, you can install a generic fuse (60 amp should be fine, and it's
to find than 80 amp). If you ever blow the fuse, you need to get a new
fan motor ASAP.
281 937 505 A = fuse box
N 017 125 3 = 80 amp fuse
443 971 845 AM = mounting bracket
N 014 128 11 = screw (x2)
N 012 005 3 = lock washer (x2)
N 011 556 2 = washer (x2)
N 013 966 12 = screw (x2)
Symptoms: Engine makes a strange rattle noise when you blip the
heard most predominantly when the rpms fall from +- 2000 rpm back down
Distributor #: 034 905 205J from 90-91 Coupe Quattro and 90-91 90
NOTES: Use very thin stainless washers to get the right spacing. You
want it too tight, the distributor must turn freely.
Mark the general direction the rotor is pointing. Timing is done by the
computer, so you don't have to be too exact.
Remove distributor. You first need to remove the hold-down bracket. You
can't really see it, but it's there. The bracket is secured by a 13mm
which may be covered by an anti-tamper cover. You will need a box
preferably a ratchet box wrench, because there is very little room to
Hold shaft by cam gear and move parallel to shaft (end play). This is
Drive out Clevis pin holding on cam gear CAREFULLY. Cam gear is plastic
and breaks easily. (Experience talking here...)
Add high quality washer/spacers between the cam gear and the body of
distributor, until there is no more play. The spacers should be
steel with an inside diameter of 12.7mm (.5"). The thickness may vary
the amount of runout.
Put cam gear back on, drive in Clevis pin.
Put distributor back in car.
New Gear Installation and Timing Considerations
I. Preliminaries: Bentley ref pgs: 3B: 28.47, early 7A:
Audi distributor alignment tool is not necessary.)
1. Rotate the engine to #1 TDC. Rotor pointing to #1 plug
terminal and0-degree flywheel mark at pointer edge. Get this right!
2. With dist cap and Hall sensor connector removed from the dist
and other junk out of the way as much as possible, note the angular
position relativeto horizontal (3B), or vertical (7A) of the Hall
sensor connector and the rotor (these will be opposite each other) for
later return to original oriention purposes.
3. Remove the anti-tamper cover, if any, on the dist hold down
clamp nut, located on the stud in the head under the dist location
hole, remove nut and clamp. I removed the anti-tamper device by
hacksawing a slot across the top of it and then unscrewing it with a
flat blade screwdriver. They usually aren't on very tight.
4. Pull dist from its locating hole, noting that the rotor turns
clockwise about 1/4 inch as the dist gear is withdrawn from its mating
cam gear. Upon reassembly it must go back in with this same final
removal orientation to end up in the same original position.
II. Plastic Gear Removal:
1. Don't try to drive out the retaining pin yet! Remove the
gear plastic from its steel hub by hacksawing 2 or more diagonal cuts
thru the plastic to the hub, pry or chew off the pieces.
2. Note that both ends of the groove pin are swaged larger than
the pin center dia. Saw off the smaller pin end and file it flush
with the gear hub.
3. Support the gear hub and shaft in a suitable V block or vice
jaws and drive out the pin using a 5/32" dia pin punch or an old nail
on the filed end.
4. Remove the gear hub and retain the shim washer pack for
5. Remove the shaft, not loosing the fiber thrust washer at the
top end, and clean the dist body and Hall rotor. If there is any
oil in the distributor, service the crankcase breather system.
(This distributor doesnot use a shaft seal component, just a
reverse spiral groove on the shaft in the top portion of the upper
III. New Bronze Gear Installation:
1. Install the original shim pack on the shaft, followed by the
new gear. Align the smaller gear pin hole with the shaft pin hole.
(Do not use the larger pin hole, it is a vendor goof.)
Support the gear hub on the far side (not on the gear teeth) and
tap the roll pin part way into the shaft. Check the dist shaft
axial clearance. It must not be tight, but should have 2 to 5
thou end play, a "just perceptable free movement" feel without binding.
If not so, remove the gear and adjust the shim pack, + or -, as
required. An additional .003" thick shim is provided with the gear and
roll pin to
faciliate this adjustment. Add or subtract different thickness
shims until the end play is the closest to the "feel" spec.
Unlikely, but if more or different thickness shims are necessary,
they can be cut from paper and added into the center of the shim pack.
2. Drive the roll pin thru the assembly and center it in the
gear. Recheck the axial clearance "feel".
IV. Distributor Installation: without VAG alignment tools.
1. Remove the black plastic shield which may have been covering
and seperating the Hall area of the dist. body from the rotor.
Not all 20V dist have this shield, which may be replaced just
prior to reinstalling the dist cap.
2. Notice that there is a line embossed on the top surface of the
Hall rotor immediately under the hot end of the dist rotor, and a
mating line notched into the top edge of the distributor housing
opposite the Hall connector and just above the Hall sensor unit.
When finally in place and locked down these two lines must line
up with each other with the engine at TDC.
3. With the dist and rotor lined up about as it was as you
removed it (you forgot where that was, didn't you?) insert the dist,
moving the rotor as necessary to get the gears to mesh. Once all
the way seated in place, while applying a slight counterclockwise
finger bias to the rotor (thus eliminating gear mesh clearance),
adjust/rotate the dist body to exactly line up the two marks, and lock
it down (lightly, you may have to move it again) with the clamp and
nut. If you are not happy with the resultant orientation angle of
the Hall connector, pull the dist just enough to free
the gears and rotate the rotor one gear tooth in the same direction
that you would like to move the Hall connector when the two marks are
again lined up.
The distributor will work in any oriention, as long as the two lines
are lined up at TDC, the actual oriention just facilitates the
electrical connections to the Hall and dist cap.
4. All 200 owners who elected to short cut and not remove the
intake manifold per Bentley, must now curse loudly at the Audi gods for
the inaccessability of the whole dist system and the dist cap hold down
clamps in particular. 7A owners need not comply.
5. "Reinstall all components in reverse order of removal".
More of Bentley's sage advice. If the engine won't start,
recheck your TDC position for accuracy and then the distributor marks
alignment for its accuracy. They must be right on. Do not attempt
to move the dist with the engine running as you did with those old
point type dist, as this dist does not determine engine ignition
timing. Thank you for flying united.
Bosch P/N 30091 is the brush/voltage regulator block, and should be
available for ~$20. You can remove the brush/Vreg block w/o removing
alternator -- just disconnect the battery and remove the two slot head
screws from the back of the alternator w/ a right angle blade
(wouldn't want to accidently short across the B+ termanal with the
connected now, would we??). New spec. for the brushes is 10mm
from the plastic, (the longest edge) and min wear spec. is 5mm.
Drill out the top of the soldered connection of the old brushes
they are not only soldered, but crimped in place, then they shoot out
their sleeves. Make sure you don't lose the springs that are behind
with the small insulator sleeves on the brush wire. Then place the new
brushes (along with the springs and teflon insulator) in the reg.
Fold the wire over so that the brushes don't try to pop out while
soldering, then try to crimp the hole the wire came through. Solder the
wires, and trim the excess wire off (~ 1.5" - 2").
Oxygen sensors have a limited life-span. Audi recommends replacing
them every 60K miles. If your gas mileage has plummeted or you've
an emissions test, you might want to consider replacing your old O2
The official replacement has the correct wires to mate up with the
but it's also over $100. You can get a generic three-wire sensor for
less, and just splice the wires into the existing ones. One common
is Bosch P/N 13913 and costs about $40. It's for some model of Ford and
can be found at most auto parts stores, just ask for it by the P/N. If
you prefer to have the original connector, you can get either Bosch P/N
13957, or NGK P/N 25040 (double-check these numbers to be sure).
Here are some instructions for replacing the sensor: (rngmeister)
Disconnect negative battery terminal.
Disconnect the two plugs from their carriers on the driver's side of
block, just to the right side of the carrier for the plug wires.
Remove battery and pop out silver insert from underside of tray
but helps with the view--may not be necessary if your sensor is in the
cat rather than the downpipe).
Tie a string around the plug, so when you pull it through, you can
the new wiring and direct it back through the same way with relative
Jack front of car up, turn wheels left to lock.
Remove passenger side front wheel. This should give you access to the
which is in the exhaust downpipe or in the front of the cat.
There are a couple of stays that keep the wires in place; open them up,
then pull the wires through and untie the string.
Loosen and remove the old sensor. You can use a 22mm offset open-end or
a box-end wrench, or you can buy a special O2 sensor socket that has a
cutout in the side for the wires.
Wipe off the downpipe so you can install the new sensor without getting
any crud on the threads. The new sensor should come with anti-seize
on the threads. If yours doesn't make sure you put some on!
Install the new sensor and tighten to 37 ft-lbs.
Tie the plug/wires to the end of the string and re-route them up to the
holder. Tighten stays to keep wire in place, making sure if there is
extra (there might be a longer wire than the original) it is out of the
way of any heat/moving parts.
Plug it back up and secure in the plug carriers.
Replace wheel, lower car down, replace battery and tray insert, connect
Fire it up and enjoy your smoother running, better gas mileage, and
Needed: metric sockets ranging from 19mm down to 12mm (one 17mm
and an extension arm may help provide leverage on the top starter bolt.
Remove lower engine compartment shield.
Remove battery cover, disconnect and *remove* battery, remove battery
on the battery shelf - you should be able to see down toward the
Remove top and bottom of air intake box, rubber intake hose, throttle
(may be optional).
Disconnect starter positive lead and black solenoid wire.
Use 19mm socket, possibly with breaker bar or handle extension to
the top, rear-facing bolt for the starter (it's on the edge of the
Underneath the car, passenger side, use a 17mm deep-well socket to
lower, front side nut which secures the starter. Make sure you hold on
to the starter--it's heavy! I think you'll need a 16mm wrench to hold
bolt on the other end to keep it from spinning.
Remove starter, save nuts, bolts, etc. Note connection points.
Install new starter in position, slip the lower bolt thru it's mounting
hole, then scoot over to the top side and hold the starter in position
while you tighten the top bolt.
tighten the lower starter mounting nut.
Re-attach wires to the solenoid.
Re-install battery, attach wires.
Re-assemble throttle body, rubber intake hose, airbox, etc.
Re-install lower engine compartment shield.
Wash hands, then start 'er up!
See also: Engine Upgrades
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