Re: 1990 V8 Quattro Idle Problem too

[paul.heneghan@bbc.co.uk (Paul Heneghan)]

>Sorry to report that cleaning the temp sensor contacts did not fix my
>car.  The temp sensor that was worked on is the water temp sensor.  I
>picked up my keys and went out to start the car after it had been
>sitting in 20 F weather overnight.  It fired and started when cranked
>but immediately died and did not want to restart.  I had the mechanic
>come out and he successfully started it by holding the accelerator open
>a small amount and keeping the Rs up once it fired and cuate.  No
>surprise, that is how I've been getting it started for some time.  He
>said that was the proper way to start the car.

He is half right because all owner's manuals for Bosch FI cars state that 
the accelerator should be slightly depressed when staring the car.  HOWEVER, 
once started, the accelerator can be released and the car should not cut 
out, regardless of temperature, milage or age of car.  There are always 
devices to increase the amount of fuel and air to compensate for cold 
starting.

>He then said I could be in
>for a lot of bucks for small improvements if I wanted him to continue
>working on it since the starting characteristics were common on Audis
>with as many miles as mine (205 k miles).

B******s.

>I guess I'll have to roll up my sleeves and go to work on it myself.

Good idea.  Here are some starting points.  Get Haynes (good for overall 
pictures, lacking on detail) or Bentley (opposite of Haynes).  Get Probst's 
book on Bosch FI.  In the absence of those, you can read my random thoughts 
on stalling while cold problems.

I don't know the specifics for your car, but there should be a technique for 
making the mixture richer at low temperatures.  On an I4 or I5 engine , that 
is done by an engine heated and electrically heated device that is bolted to 
the engine just below the spark plugs.  This fiddles with the FI control 
pressure.  It is identifiable because it has a couple of fuel lines going to 
it, an electrical connection and sometimes a vacuum feed.  This is usually 
fairly reliable (recent posts might disagree with this).

There will also be a device to simulate the effect of keeping your foot 
pressed slightly on the accelerator.  This usually results in an idle speed 
>1000rpm when the engine is cold.  This device gradually reduces its effect 
as the engine temperature increases.  On an I4 engine this is often a 
throttle bypass with a bimetallic strip which allows more air through when 
the engine is cold.  On an I5 engine, the throttle bypass is usually 
controlled electronically by an Idle Stabilizer Valve (ISV).  This is 
usually mounted near the back of the engine (the bulkhead end) on the 
manifold side.  It is often a large cylinder (3cm diameter 15cm long from 
memory).  It has a couple of air connections and an electrical connection.

The ISV is notorious for having bad electrical connections (causing engine 
cut out when cold).  It also has a habit of gumming up, particularly in high 
milage engines when a lot of oil and crap seems to get into the air intake 
(engine breather hoses).  This usually causes the car to almost cut out 
(excuse split inf.) but then recover at the last possible moment.  Carb 
cleaner often sorts it out; if your feeling wealthy, you could consider 
buying a new one.

I have also had the control relay for the ISV blow up.  This is either a 
stand-alone module (about the size of two standard-sized relays) or built 
into the ECU (in newer cars - probably your case).  This gets inputs from 
rpm, temperature and throttle closed switch, and produces a PWM output to 
drive the ISV - i.e. an output which switches between 0 and 12V very rapidly 
(about 4000Hz on my cars).

The first step in fault finding is this:
When you've got the car running, and warmed up, try unplugging the 
electrical connection to the ISV.  If the revs do not change, then ISV is 
not doing its job.  It could be an ISV problem, a controller problem, or an 
input to the controller problem - I hope that's vague enough for you.  An 
AVOmeter is probably required for more precision.

Good luck.  Let us know you get on.

Paul
paul.heneghan@bbc.co.uk
1984 Audi 80 quattro (ISV controller replaced by Studer capstan control 
circuit)
1989 Audi 100 Avant (ISV badly in need of a clean)