Owing to the limitations in the IOS Bluetooth stack, make sure what you buy is ELM327 with WIFI version rather than the Bluetooth one, unless you have jailbroken your phone and know what you are doing.
Wifi elm327 iphone can be ordered from Eobd2, which was sold at a very reasonable price — €13.00 (free shipping). Here list detailed steps on how to use an iphone or ipad touch with ELM327 OBD tool as follows:
1. Connect the ELM327 to your car.
2. In the settings on your IOS device, select to connect to a WIFI network. It is rather relatively to find out which one you should be done. For example, my ELM327 is called “CLKDevices”, but yours may vary.
3. Once connected to the WIFI network, then you can set the IP address. Configure the IP address to 192.168.0.123 and the subnet mark to 255.255.255.0 (NOTE: Do not set your IP as router).
4. Start your car, the OBD II port was providing power to the ELM327, but in some cases you will not be able to retrieve any data from it if the is not started.
5. In the APP, configure the connection to use a custom TCP connection with IP 192.168.0.10 and TCP Port 35000.
6. Enjoy reading all this information on your car better and cheaper than by using the crappy scanners they sell in stores.