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Re: Stalling on 1990 200 tqw


Your symptoms also sound typical of a vacuum leak, I posted
a list of things to check on these cars sometime ago. Here
is an excerpt from that post.

The ABC's of Running High Boost 
 SJM Jan. 1997

"BEFORE" you do any Turbo boost mods to your 86-90
5000/200TQ Audi please read the following. 

The low cost of these quattro list ECU mods do not allow
for much technical assistance after the sale. It  should be
your responsibility  (or your mechanics) to check out and 
verify all the system components are working correctly
before you do the ECU mod and raise the boost. Obviously  a
tune up, new plugs, fuel filter, air filter, oil change
etc.  should done before stressing the engine with more 
turbo boost.

You need to make sure your engines various breather/vacuum 
hoses and turbo intake and pressure hoses are in good
shape. Leaks anywhere in these hoses can cause lean or rich
running and poor starting. Vacuum leaks would typically
cause lean running, pressure leaks after the turbo could
cause slightly rich running. It is  NOT sufficient to just
visually  look at these hoses without first removing them! 

The large breather hose coming from the side of the engine
up to the valve cover typically gets rotten on the inside
part of the hose facing the engine block. The small T hose
connecting the  two hoses to the valve cover also gets
rotten from the oil mist flowing through it and will crack
on the back side. The other hose connecting the  intake
boot to the valve cover  should be removed and checked. The
two small  idle stabilizer hoses should be removed and
checked also as they can get blown off from the pressure. 
Any of the smaller hoses connected from the  intake
manifold to the heater/AC system should be checked for

The valve cover gasket, the dipstick seal and the oil cap
seal should also be checked and can be a source of a vacuum
leak. Even the  front and rear crankshaft seals along with
the camshaft seal can be the source of vacuum leaks (this
is less likely)  The rear crank seal will sometimes
"squeal" when the car is first started because it is
leaking and allowing air to be sucked past or because it
has no oil on it at first. Removing the dipstick with the
engine running usually silences this  "squeal". Sometimes
pushing in the clutch will also silence this squeal.
(Pushing in  the clutch moves the crankshaft slightly) Ned
Ritchie at IA published a tech  tip in the QCUSA quarterly
newsletter regarding this problem.

 The accordion style hose that connects the intercooler
exit to the intake  manifold  usually rots (from oil) and
cracks at the bottom between the ribs. Remove  and check
it. The turbo  intake hose that connects to the metal pipe
and the  turbo exit  (pressure) hose going to the
intercooler should both  be removed and  checked  as well. 
The later 200TQ's with the smaller K24 turbo have some
"insulation foam" inside this pressure hose going from the
turbo to the intercooler and  sometimes this insulation
will come loose and get blown into the  intercooler.
Sometimes  the hose clamps for these pressure hoses are
just loose and under high boost will leak. 

You may also want to check the cold side turbo shaft for 
excessive play and  look for any metal shrapnel caused by
worn turbo bearings allowing the blades to rub against the
turbo housing. The main fuel distributor  rubber boot
should be visually checked for cracks with a flashlight and
a  mirror especially around the edge where the large clamp
holds the boot to  the fuel distributor opening. The decel
valve located on the CIS air box assembly (behind the
fender) and large rubber hose going to the fuel distributor
rubber boot could also be the source of a vacuum leak.
There are also charcoal canister purge valve(s) (late 89
has two)  that should be checked for correct operation.
The intercooler end cap seals can leak and you may want to 
install some  straps  around the intercooler to hold it
together under high boost. The internal  intercooler rubber
seal that  seals the internal upper and lower sections of 
the  intercooler should be checked when  you remove the
hoses from the  intercooler. You should look inside the
intercooler and make sure this seal has not  blown out
which would allow the air entering the intercooler to
bypass the  intercooler and go straight into the intake
without any cooling effect. 

The fuel injector inserts that are screwed into the
cylinder head may need to be replaced along with the rubber
o-rings sealing the fuel injectors.  The green Viton
injector o-rings should be used instead of the older black 
rubber ones that get hard and don't seal well over time.
Leaky injectors can  increase the hot/cold starting times.
Dirty/clogged injectors can cause poor low end performance
and uneven performance when cold. Intake valve carbon
deposits can also cause cold running problems as the carbon
acts like a  sponge, soaking up the fuel at first. You
should look at the back of the  intake valves when you
remove/replace the injector inserts. With severe carbon
buildup some repair shops can use a walnut shell blasting
device to clean off the carbon buildup. Lighter buildup can
be removed with the use of a fuel additive or a fuel with

To repeat:
 Vacuum/pressure leaks anywhere in all of the above
mentioned areas may cause lean/rich running and hard
starting. You may also want to have a mechanic check that
the CIS fuel injection system pressures are correct. After
verifying there are no  vacuum/pressure leaks, and the fuel
system pressures are correct,  the basic idle mixture
should be  checked and  adjusted if necessary.   This can
be done by either measuring the CO% of the upstream exhaust
gas (O2 sensor disconnected and using the exhaust analyzer
connected to the small metal pipe with the blue cap) Adjust
the upstream CO% to be around 1.2% using the Bentley
procedure for your  model car. The later 200TQ's use a
slightly  different procedure. You can also adjust the idle
mixture by measuring the  duty cycle of the  CIS  frequency
valve that is used to tweak the mixture. This assumes  the
O2 sensor is connected, working correctly and is warmed up
(O2 heater working ok) . Again,  follow the Bentley
procedure.  Even though this duty cycle changes  back and
forth between  different  values usually the  "average"
duty cycle  should be adjusted to be  around  38%.  This
corresponds to a upstream CO% around 1.2%. Getting this
adjusted  correctly is very important to ensure good
initial cold running and  is required for correct full
throttle enrichment  under high boost! 

The throttle switch which provides idle and full throttle
information to the ECU should be tested for correct
operation as this part typically develops poor internal
solder connections which may cause strange idle behavior.
The plastic cover can be cut off and then you need a
magnifying glass to view the cracked connections. The idle
stabilizer valve (ISV) can also stick from oil/crude built
up inside. Cleaning the ISV with carb cleaner may help. A
defective throttle switch can also prevent the correct
operation of the Waste Gate (WG) solenoid system that the
ECU uses to adjust the turbo boost. The wastegate control
hoses should be checked for cracks! The large main hose
coming from the intake manifold and  going to the lower
chamber of the WG delivers pressure to open the WG. Leaks
in this hose can cause overboost conditions! The small
hoses connected to the WG solenoid and WG should be
checked. The  internal WG diaphragm can also develop leaks
and may prevent correct operation of the WG. . A defective
full throttle switch will also prevent the ECU from
changing the mixture under full throttle. The ECU increases
the fuel to the engine by using a higher duty cycle for the
frequency valve under  2/3 to full throttle conditions. The
air temp sensor that the ECU monitors can have poor
connections or can be  intermittent on these cars as well.
This sensor is located on the intercooler exit.

The self-diagnostic system test should be run to make sure
that  there are no other faults in the engine control
system. You need to do a 3rd gear full throttle run to
exercise this diagnostic  system correctly. The car should
not be shut off after doing this full throttle run on the
86-88 1/2  5000TQ/early 200TQ's as the fault memory will be
erased. The later 200TQ's with dual  knock sensors (MAC14
ECU) have a non volatile memory for the fault codes that
can be read later even if the car has been  turned off.
Check the Bentley procedure for more info.
TEXT DELETED for brevity

Scott M.
89 200TQ