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Old 06-09-2013, 03:03 PM
1st Gear
Join Date: Jun 2013
Posts: 2
Default '01 TT P1639 and high RPM

Upon starting the engine the RPMs climb to 2000 and then slowly increase to around 3000RPM all while the accelerator pedal is fully released. EPC light is on and the only fault code my generic reader is showing is P1639 for accelerator pedal implausible signal. If while the engine is running at 3000RPM I depress and hold the brake pedal, the engine returns to idle ~700RPM, then back to 3000RPM after releasing brake pedal.

The whole issue with the car started when I floored the accelerator one day which caused the EPC light to come on and go into limp mode. I originally had fault codes for O2 sensor after catalyst heater circuit and one for system bank 1 too lean (ended up being a vacuum leak i have since fixed). After disconnecting he 4pin connector for the O2 sensor after catalyst, I found what looked like engine oil inside. I work on diesel engines for a living and I have seen on numerous instances coolant being wicked through harnesses due to faulty coolant level sensors. I also have what looks like a leaking power steering pressure switch that is leaking oil into its connector. Anyone ever heard of oil wicking to the O2 sensors before? I went ahead and cleaned the O2 sensor connector and replaced the O2 sensor, cleared the fault code and it has not returned.

We have done all vacuum, fuel pressure, spark and compression tests and everything is normal. I have noticed as well that the throttle body valve does not open all the way with the accelerator pedal fully depressed (key on, engine off) it opens only about 1/4 of the way. I do not have access to a VAG-COM so I did the whole battery disconnect, key on for 15min to manually set the throttle adaptation but fault code P1639 is still active.

From all the testing I have done it seems like I have either a bad throttle body or the ECU was damaged from the O2 sensor issue and the circuit for accelerator/throttle (that is damaged) is being ignored when I depress the brake pedal, causing it to idle properly. How do I tell if its a bad ECU or not?

Any help would be appreciated, thanks.
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Old 06-09-2013, 03:06 PM
1st Gear
Join Date: Jun 2013
Posts: 2

Forgot to mention, I have already replaced the accelerator pedal and also ohmed out the harness from the pedal to the ECU and found resistance is in range. Also checked voltage supply pins at pedal and found 5v on both supply pins using chassis ground and circuit grounds, so I don't think I have a harness issue.
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1639, accelerator, audi, brake, code, disconnected, implausible, p1639, pedal, pin, signal, smith, tt, voltage

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