[Biturbos4] Throttle position sensor problem

[Grant Lenahan]

BTDT on my 2000 S4.

here's what I found.

The typical fault you will get is called "epc" and a light should  
come.  epc is electronic pedal contgrol, or drive by wire.

When a fault in the fly by sire system is detected the system goes  
into limp mode, which you experienced. It was happening to me every  
day. It resets with an ignition cycle.

What i found is that the throttle butterfly, which is controlled by a  
stepper motor, slowly builds up crud inside the TB, much like an old  
carbon composition potentiometer in a hifi. I posited that thsi was  
the case, and tried the same old cure:

1. clean with carb cleaner by spraying inside the TB
2. loosen/clean the TB inside by exercising the butterfly completely  
through its angle of motion, several times, quickly. This creates a  
wiping action.

It worked.

You can infer that one of the problems I had run into was that teh S4  
basically had too much power for normal driving, and i almost never  
went WOT.  So junk built up.  Its another case of cars must be driven  
as intended, at least occasionally.

Hope this helps,

Grant
On Oct 26, 2008, at 11:01 AM, Richard van der Hoff wrote:

> Hi guys,
>
> I've been having a bit of trouble with my 1999 S4 biturbo, and was
> wondering if anyone had any experience with similar problems.
>
> The symptoms started with an intermittent engine fault light. I  
> plugged
> in the VAG-COM and the problem seemed to be
> "17581 - Angle Sensor 2 for Throttle Actuator (G188) Signal too High
>              P1173 - 35-10 -  -  - Intermittent".
>
> Now, I've monitored the offending sensor in VAG-COM, and it appears to
> move nicely up and down with the gas pedal. I've also checked for  
> loose
> or corroded connections between the sensor and the ECU, and taken  
> apart
> the sensor and checked for damage inside. All came up blank.
>
> So I put it all back together, thinking "it'll either fix itself, or
> become worse until it's obvious what the problem is".
>
> So yesterday it got worse (on the way to a friend's wedding, of
> course...) - and I lost pretty much all power; basically the engine  
> shut
> itself down to a fast idle. Fortunately after a restart it ran fine  
> again.
>
> I limped it back home today - the problem seems to be getting more
> regular, and have pulled the codes again. I now have, in addition  
> to the
> original fault:
>
> 17950 - Angle Sensor 1 for Throttle Actuator (G187): Implausible  
> Signal
>              P1542 - 35-10 -  -  - Intermittent
> 17965 - Charge Pressure Control: Positive Deviation
>              P1557 - 35-00 -  -
>
> So presumably both throttle sensors are out of spec at once and the
> engine is shutting itself down to a safe state. I'm hoping P1557 is a
> symptom of the other problems, otherwise it looks like I have a boost
> leak to add to my woes.
>
> In short, does anyone have any experience with throttle-sensor  
> problems,
> any joy in fixing it, and if (as I suspect) I need a new throttle
> sensor, is it possible to obtain one without the entire throttle body?
>
> Thanks
>
> Richard
> _______________________________________________
> Biturbos4 mailing list
> Biturbos4 at www.audifans.com
> http://www.audifans.com/mailman/listinfo/biturbos4