The car is a 2004 A4 1.8T coded AMB. Several months ago, the engine lost power, idled rough and then high, and revved up and down at will. I pulled three codes from it using a scanner:

P0638: Throttle Actuator Control Range/Performance (Bank 1)
P0221: Throttle/Pedal Position Sensor/Switch B Circuit Range/Performance
P0507: Idle Air Control Systems RPM Higher than Expected

I tore into the engine and found cracked PCV tubing, split vacuum lines, and a dirty TB. I replaced the tubing, split lines, TB, and the blow-off valve that the previous owner had installed with a stock TT diverter valve. The problems went away for about a five mile drive but then returned. I didn't rescan it. Next, I replaced the accelerator pedal with a new one. Same issue. Lastly, I bought a KKL cable off Amazon and VCDS from Ross-Tech. The software is communicating fine with the car (or so it seems). I cleared the codes and the car ran fine for 30 miles but is now acting up again. I tried to complete a TB adaptation but the far right-hand box says ERROR. I've tried it many times and some of the time it would say ADP RUN but most of the time it just says ERROR. I get two codes now:

17579 - Angle Sensor 2 for Throttle Actuator (G188) Implausible Signal P1171
17987 - Throttle Adaptation (J338): Adaptation Not Started P1579

When I attempt to clear the codes, 17987 won't clear and the other one will come up as soon as the engine is started.

Could it be the KKL cable, the brand new TB, or something else entirely? The TB flap does move when the throttle is pressed and I can hear it actuating at times, but I also hear a slight buzzing or humming noise from it when I turn the key on. Also, not sure if this matters, but I did notice the other day that my brake lights were on when the brakes weren't--I changed that switch almost exactly one year ago--so maybe it is some other electrical problem.

I'm sorry for the long post and I hope it doesn't scare anyone away. Any suggestions?

 

Wilkommen to the forums!

hrmmm....

sounds like an electrical problem to me. check to make sure things are plugged up tight. not sure where exactly this "G188" sensor is but it sounds like it is not receiving the proper power or signal (loose connector or bad wires).

as for the throttle adaptation, if there is a loose connector/bad wire somewhere, i imagine that would cause the problems you are describing. if you can't get it done with the vagcom you may try the "manual" adaptation procedure. disconnect the battery for 10 minutes. reconnect. turn key to the on position (DO NOT START). you should hear the some clicky whirring noises under the hood as the adaptation is performed (about 2 minutes i think). turn key off and remove. start car.

the manual adaptation procedure I'm doing from memory so I may have it a bit wrong. a search should help.

good luck

 

Thanks for the ideas, 02A6Beau. I'll try disconnecting the battery and see if that solves anything. Since I still have my old throttle body, I'm going to clean it up and install it and see what happens. As far as wiring problem, is there anywhere along the harness that is particularly prone to problems?

Anyone else have any ideas?