Finally, with a new Arduino (actually the third, we burned the second, putting 9V on it with the motor shield, because YUN don't have a regulator as the other Arduino, but we didn't know that) we are working on the project again.
I took a video a hosted it on youtube: Control car by wifi using Android and Arduino - YouTube
We worked on the documentation these last weeks, couldn't work on the arduino (I just got the new one) and it's on github!
GitHub - Vadorequest/AAD1: Car controlled by Wifi, using an Android application
I have a new problem but I'll create another topic about it. (parsing)