Replacing the air temperature sensor has made no difference. The new part looked the same as the old part, with a small part of the metal exposed, so it must be designed this way.
Three other jobs that I will do before I give up and take the car to a dealership for a proper diagnosis are as follows;
1. The throttle linkage is filthy, and needs cleaning. Also there appears to be some play (is play normal?), and I will check the operation of all the joints, and how the linkage interracts with the throttle switch, and what effect this has on the idle. Perhaps the throttle linkage sticks, therefore the switch sends a signal to the ECU saying the engine is not at idle.
2. Check movement and position of the airflow sensor plate. Clean airflow sensor plate and inside of housing as this is dirty with some filmy type discolouration.
3. Replace air filter, which is dirty, and does not appear to have been replaced for some time. (Will hinder hot starts)
Any further suggestions welcome.