Right I've got a PLX KiWi WiFi and its been doing the usual dropping out every minute or so for a minute, tried loads of different settings and seem to have come across what seems the winning combination, well for now and thought I'd share it for others to try:-
Iphone 4.0 with version 4.3.5 (8L1) not tried the latest version.
My settings are:-
Airplane Mode: OFF
WiFi: ON
Network PLXDevices
STATIC
IP Address: 192.168.0.11
Subnet Mask: 255.255.255.0
Router: 192.168.0.10
HTTP Proxy: Manual
Port: 35000
Ask to join Networks: ON
Other settings:-
Personal Hot Spot: OFF
Notifications: OFF
Location Services: ON
Bluetooth: OFF
Car is a 911 C2S 2006, I get between 1.4-1.8GHz update speed and with the above settings drop outs seem to have greatly reduced and shall do more testing. I've position the KiWi WiFi in the centre console of the car as well as that seems an ideal out of the way position.
This is my settings which seem to work best so far and shall do more testing, be good to hear from others if these settings help or what settings you have found yourselves work best?
I've heard some download apps to prevent Iphone looking for other wireless devices, if so what are these apps and any other tips would be great and to compile them all in this thread.

Lastly are the bluetooth OBD readers any better, as I see PLX have a KiWi Bluetooth, is this more reliable and does it work with Harry lap timer pro on Iphone?