he encontrado esto en la pagina de jiayu para "reparar" el wifi.. lo habeis probado alguno a ver si soluciona lo del wifi que va y viene?
Link
Parece que soluciona eso:
It turns out that, in some countries, if you have a SIM card in your Android 4.0 device, Wifi doesn’t work like it should. Apparently, there’s an issue specifically with the Wifi country code that causes the problem. Fortunately, XDA Member fardjad has isolated the issue and offers a fix with his free app, Wifi Fix for ICS--> en el GooglePlay es: WiFix Manager.
If you have a rooted phone, all you need to do is install the apk and grant the app SU permissions. The app will, from this point, run at startup and fix any issues you might have previously had connecting to a Wifi network when there was a SIM card installed in your ICS device. Several users have already reported an immediate difference in Wifi performance.