[sly]

That's a CAN Bus communications failure code. It's possible that something is corrupting communication to the ECU. Are there any aftermarket mods to the car? It could also be loose ground connections.

I'm seeing that it could be caused by a loss of communication to the ABS module. Perhaps triggered when you disconnected the battery. Can you clear it and does it come back? Do you have the traction control light indicating an error? If you lose traction and stability control, it could possibly cause a fast idle if the ECU is in limp home mode to keep it from stalling.