Novice + Boost issue = ?No Hope?

Brett Dikeman brett at
Wed Jul 3 00:28:50 EDT 2002

At 7:56 PM -0400 7/2/02, ALPHA1220 at wrote:
>Here is my situation, maybe some more experienced people can help, since my
>moderate level of knowledge concerning car mechanics hasn't gotten me very
>far. I have been driving a 1991 200 20v quattro for approximately 9 months,
>having taken it out of storage (My Dad drove it from 1991-1995)

Get the T-belt changed as soon as possible...the current belt is at
the best AT the limit for age(timing belts have both age and mileage
limitations; 7 years, 60k/miles.)  At the worst, the belt is 10+
years old.

>. For as long
>as I have been driving the car, I have never gotten maximum boost: 1.4 was as
>high as I was getting in the summer and fall of 01', 1.3 in the winter and
>spring, now down to 1.2. When I first began driving the car, I noticed what I
>thought was an issue with finicky clutch engagement: coming to a stop
>following hard acceleration would often cause my car to stall (an embarassing

This is caused by a tear in the membrane of the turbo bypass valve,
which normally opens after the throttle snaps shut under boost(ie,
when shifting or suddenly braking), routing air from the outlet of
the turbo directly back into the inlet of the turbo, keeping it
spinning(otherwise, the turbo slows dramatically.)

>  probably just pulled up the specs for a 200 10v and assumed I was
>getting max boost).

Quite possible.

>So my question is twofold:
>1. What is most likely wrong with my car, and how do I confirm it?

The turbo bypass valve is the most likely candidate.

>2. What do I need to do to fix it and return my car to a normal op. specs.
>(If possible, I'd like to do it on my own, so anyone who can give me specific
>instructions, please do so.

Replacing the valve is relatively easy; it is -really- easy with a
socket driver handle, flex extension, and a 6mm(at least on my car)
socket; once you use this on the clamps on the car, you'll never try
a screwdriver makes undoing clamps a breeze if you have it.
   The valve is directly in front of the turbo; plastic, round, two
large ports and one small vacuum line connection.  Undo both hose
clamps, pull the valve off(don't be afraid to wiggle/pull, that
rubber is very strong.)

   Replace the control line for it as well; this line runs under the
large intake pipe that comes up from the intercooler; notice the hot
exhaust right underneath there?  Guess what that does to the rubber
vacuum line :-)  Usually it becomes so brittle, you can break off
small pieces of the hose like hard candy.

The most permanent solution is one of the following:

-reroute the line along the edge of the engine compartment
-use a piece of copper line(such as what one would use to hook up a
fridge's icemaker) for the length of the run that is above the

Home Depot and most other hardware stores sell small "wide band"
spring clamps that are just a clamp made out of spring metal that you
open up by squeezing the ends with a pair of you'll see,
the connection is recessed and a screw-type clamp will not fit.

Hook up the vacuum line, put the valve back in, tighten clamps...done!

That will solve the stalling problem.  Low boost probably is a
separate issue; if the low boost is NOT accompanied by
stumbling/surging*...while you're down in that area, see the little
solenoid valve?  Has three connections on the bottom.  If you have a
multimeter, measure the resistance across the two terminals of the
valve.  It should be 28-30 Ohms; if it is more like 300, you need a
new wastegate frequency valve(WGFV for short)

If the valve is within specifications, then does the air conditioning
run?  If not, unplug the temperature sensor underneath the intake
manifold; you're looking for the larger of the two hanging down from
a metal pipe(not the one with two separate big
boot.)  Test drive the car.  Boost up?  Then your Multifunction
Temperature Sender(MFTS for short) is shot; these are also a common
failure item, sending a false overheat signal to the climate
control(shutting off AC) and the engine control unit(which restricts
boost to keep the engine as cool as possible.)

If it turns out to be none of the above, then my next suggestion is
either to take it to a mechanic who knows 200q20v's(see below) or if
you still want to pursue it on your own, pull the fault codes from
the engine control unit; this is outlined very nicely at will need to construct a test lamp using an
LED; Scott M's site explains all this.)

*if the car stumbles/surges/bucks under boost, you've got a split
hose or other major vacuum leak.  One very good canidate is the
"michellin man" hose that goes from the intercooler to the metal
intake pipe; remove it, clean it up with dish soap or simple green
etc...and inspect under good light for any tears or splits.

>  If not, tell me how to find a reputable place to get my car fixed).

Can't help you in this department...but I'm sure we have a lister in
your area.  If you don't get any answers, try reposting just this
question only with the subject line "mechanic needed in ____ area".

Feel free to post a followup from what you find from suggestions
above(and any others you get of course!)

"They that give up essential liberty to obtain temporary
safety deserve neither liberty nor safety." - Ben Franklin

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