Thanks for that info. It gives me something to check rather than just put a sensor in and hope it does the job. The picture in your link looks the same as the pictures I have been looking at.
Just a thought after reading your post, you mention 2 pins, 1 with voltage on it and the other to earth. I notice in the picture that the plug has 4 pins, I'll put a meter on the pins and see what I get.
1 bit I have read says that inlet air temp and density information is provided by a "temperature and manifold absolute pressure (TMAP) sensor".
Is this a dual unit providing 2 lots of information to the PCM?
It looks like a Ford dealer is the only place to get one over here, none of the motor factors seem to stock them.

Thanks again, I'll have a look on saturday and see what I can find.