I use the free version of Torque - Torque Lite - with my Samsung Galaxy A7 and it works perfectly with an Elm327 plugged into the OBD2 port.
Heaps of Elm327s out there on Fleabay but best to get one of the more reputable ones rather than a cheap Chinese knock-off, even the good ones shouldn't be much more than $25.
Heaps of Elm327s out there on Fleabay but best to get one of the more reputable ones rather than a cheap Chinese knock-off, even the good ones shouldn't be much more than $25.