Rick.Cook23@yahoo.com

2000 A4, 1.8t, 5speed, ATW motor

When I turn on the ignition, without cranking the car - I can hear a high
pitched whining sound coming from the throttle body. I've disconnected
the battery, let it sit overnight, reconnected - thinking that would reset
the throttle body adjustment - nothing. Same whining - same cranking
and sputtering - but no starting.

Anyone have any ideas?

gsjohal

When the ignition is turned on, sounds like the ecu is trying to re-adapt the throttle unit to restore its values. The throttle body is probably defective, as it is whining excessively and not stabilising to allow the car to run.

Rick.Cook23@yahoo.com

I'm off to the salvage yard to see if I can get another throttle body. Not sure if the salvaged one will be any good or not - but it's only $20 to find out. Updates soon...

Rick.Cook23@yahoo.com

Well, replaced the throttle body - same exact deal. Turn on key, throttle body "whines" for a few seconds than stops, but when I try to start car (again, 2000 1.8t ATW 5speed), it sputters
and acts like it wants to start - but doesn't. :-(

I have checked all fuses (all of them), fuel pump is good and spinning up, replaced fuel filter, checked for spark (had it, but replaced plugs anyway), all good. Codes are telling me air intake temp sensor and engine coolant temp sensor - but replaced (yes - the green coolant temp sensor - not the blue).

So, hopefully this will help others out...

I took the air intake temp sensor - from the wiring, it's the simplest. Only 2 wires for the
air intake temp sensor. One wire, I believe, is supposed to carry 5V into the sensor (#1).
Then, the ECU is supposed to be monitoring the output voltage of the sensor - which varies
with temp.
V = IR(t) where R(t) is resistance as a function of temperature
Long story short - I believe wire #1 into the air intake temp sensor should have 5V.
I've measured mine and it's actually 4.68V. But here's what I'm thinking, with the
connector DISCONNECTED from the sensor - I should see the 5v (or 4.68V in my case)
on wire #1 - but nothing - 0V on wire #2 (because it's disconnected and therefore there
should be no circuit - just wire #2 leading back to the ECU). But in my case, I actually
DO have current on wire #2 when the connector is disconnected!! I think that is bad.
I actually read 4.84V on wire #2 - when (I believe) it should be zero.

I think the wire insulation between the two wires is cut, or melted, or something that is
allowed current thru from wire #1 to wire #2 even when DISCONNECTED. And since I
am having the same problem with engine coolant temp sensor (even replaced with new
part) - I believe it is happening some place in the harness where both the air intake temp
sensor and engine coolant temp sensor wires are touching. So my job is to find that
place - and fix it.

Please let me know if you think I'm on to something here - or if I'm on the wrong track.
More later...

Rick.Cook23@yahoo.com

Okay, if anyone is following along, I could sure use your help...

Quick recap: 1.8t ATW in a 2000 Audi throwing multiple codes. Turns over, sputters, but
will not start. I've checked codes and all the usual suspects are showing up: engine
coolant temp sensor (replaced with new, green), air intake temp sensor (replaced), engine/crank speed sensor (replaced), cam position sensor (replaced).

Using code reader, not only do I see all these codes, but it's telling me the intake air
temp is = -40 and engine coolant temp is = -40. Neither is correct. :-) So I focused
just on the air intake temp sensor since it only have 2 wires - one that carries a 5V
signal to the air intake temp sensor (measured, my is actually 5.05V), goes thru the
thermistor in the sensor (varies resistance inversely to temp), and carries signal back
to ECU on wire 2.

When disconnected from the sensor, I measured 5V on wire 1 coming in - good.
But while still disconnected, wire 2 measured 4.68V - what? That should be zero - ground -
when disconnected from the sensor. But nope - it read 4.68V. So, I thought I had a
short on wire 2 somewhere. I took the entire wire harness apart looking for the short -
nothing. I measured again directly where wire 2 goes into the ECU - 4.68V.

So finally, I got brave. I couldn't see an short that allow current into wire 2, so I cut
wire 2 about 2 inches from the ECU. Then I measured both ends of the cut wire.
out at the disconnected sensor and at the end I cut - sure enough - zero volts. But
on the 2 inch wire still connected to the ECU - the same damn 4.68V!!!

So, somehow, what should be zero at the ECU is consistently reading 4.68V.
A power to ground short? But directly from the ECU?? I went to salvage today and
got another ECU. Now, salvage part may not be good - but what are the odds - it
has exactly the same voltage on wire 2 - 4.68V.

Who can help? Please - something is wrong and I can't figure it out.

Articus

If you have access to a hair dryer, pull the intake air temp sensor out and blow on it with the hair dryer, measure wire#2 to see what it is doing when you do this. You might need a helper to juggle all of this.

Are you doing these measurement with the car in the Key On position?

No voltages from sensors etc can really be trusted in any electronic system when the ECU is in the "Off" state.