[V6-12v] all quiet on the AUDI Front

[James4ihl at aol.com]

Tom and Clive --

Thanks for the info. Fortuitous that you should happen to have mailed me that 
info today as I spent most of the day stripping down the intake vaccuum 
system, which also gives me (rare) access to the throttle valve unit and connector.

To stick with this topic for a second, I tested the throttle resistance today 
and didn't notice any appreciable 'dips'. However, I'd agree with Tom that 
the meter may not respond quickly enough to catch any of the dips for this 
particular problem. I've noticed that my multimeter takes a second or so to 
respond, and that's generally the duration of the dip. Maybe it's because I've got a 
relatively cheap consumer digital multimeter and that pro ones give you a 
faster response. However, the immediate thing that I need to ask the list, quite 
urgently as I have to put the intake air plenum back on tomorrow, is this: when 
I unplugged the connector to the throttle valve unit, I was surprised, in 
that on the throttle pot connector itself (the one actually on the throttle pot) 
is a six-pin connector. All well and good. However, on the connector to the 
engine control unit, contact 5 is missing. I just need to ask whether this is 
normal, or whether one of my contacts has pushed itself back into the holder! I 
do find it odd that you'd have a six pin connector and then just not have one 
pin in the middle of the corresponding connector... I mean since it was 
designed for that ignition system, why not just have a 5 pin connector and be done 
with it?! Could anyone tell me, fairly urgently whether this is normal or not? 
The connector is fairly innacessable, so I'd rather not try to pull back the 
rubber grommet unless I have to, to check whether there's a stray contact 
inside!

Obviously, if the contact IS supposed to be there, this could be the cause of 
my problems!

Tom, the contacts look shiny and clean, but I'll give 'em a good spray of 
Deoxit and plug/unplug them a few times to make sure. Your theory of the contact 
'bouncing' makes sense and what you describe about this 'confusing' the ECU 
seems to describe what happens in that the car stays at the same revs, as though 
the ECU is thinking 'uh... so... what do you want me to do, exactly?' until 
it gets new 'clean' information by you either pressing further on the throttle 
to a 'clean' area, backing off the throttle again to a non-broken part, or 
until it gets wiped clean.

A second (and third) question regards the vaccuum system. Has anyone else 
found that their vaccuum system doesn't correspond to the system in the manual? 
Mine has quite notable differences:
a) I can't see a vaccuum connection to the brake servo (in fact, now I'm 
looking for it, I can't see anything resembling a brake servo on this car (yet the 
brakes work fine).
b) It looks like I'm missing at least one 'non-return valve' just next to the 
fuel pressure regulator. I just have one next to the intake manifold 
changeover valve.
c) The non-return valve I do have doesn't seem to work in either direction 
(at least not with the amount of pressure I can generate with my lungs to blow 
into it)
d) On the intake manifold changeover solenoid valve (electric, not the 
vaccuum operated valve) there are two plastic vaccum hose connections and then a 
metal 'connection' coming out of the front. This metal connector is 'plugged' by 
a plastic plug, but when I blow into the valve from one of the other 
connectors, this plug doesn't seal the connector. I pulled it off and it's designed 
with slits cut down the inside so that it delibarately doesn't seal this 
connector, but is this an original plug designed this way, or should this connector be 
sealed tight?

I know that's a lot of questions, but mainly I'm asking 'how do these things 
look on your car' because I don't have another V6 locally to compare, and the 
Audi diagrams don't describe the system on my car completely accurately!

Thanks guys
James

In a message dated 27/3/04 5:25:54 am, tomchr at ee.washington.edu writes:

In the past I have checked the sensor the following way although I am not 
sure of AUDI config

  1 pin is ground

 1 pin is =5 volts

 1 pin = signal out

 you should be able to put a voltmeter on signal out and ground and watch the 
voltage change as you change the throttle position. you should have a steady 
increase in voltage up to about 5 volts , which is "flood" condition to the 
ecu with no drop outs of voltage. If you slowly open it and find the voltage 
drops off at somepoint you have found your problem. I think Tom may have a bently 
with the info you need.

> Eh... I guess that should have been pin 1, 2, 3...
> 
> >you should be able to put a voltmeter on signal out and ground and watch
> >the voltage change as you change the throttle position. you should have a
> >steady increase in voltage up to about 5 volts , which is "flood"
> >condition to the ecu with no drop outs of voltage. If you slowly open it
> >and find the voltage drops off at somepoint you have found your problem. I
> >think Tom may have a bently with the info you need.
> 
> You may not catch any discontinuities with a voltmeter or ohmmeter. The
> sampling time of the meter (and the response of your eyes) isn't fast
> enough. What typically happens as the pot wears is that the wiper will
> 'bounce' on the resistive track. The bouncing happens pretty fast and won't
> necessarily show up on your meter. But it will confuse the ECU.
> 
> James: Before buying a new throttle pot, check the connector. Give it a
> good cleaning with contact cleaner.
> 
> Tom