auto choke sensor vauxhall frontera sport?

Hi there.
The frontera sport does not have a choke sensor as such, it uses info from the coolant temp sensor and the air intake temp sensor to judge how much enrichment should take place.
If you disconnected the battery when you replaced the coolant temp sender unit, the data in the ecu was probably reset to the original spec set by the manufacturer, and after a while the ecu learns about it's environment and the driving styles as it is used.
It sounds like you might have a sticky idle speed control valve or possibly the throttle position sensor has quit, but I would check the idle speed control valve first. It is locate between the plenum chamber and the throttle butterfly valve. Take it off carefully and hold the inner and outer together until you are at the bench, then seperate and clean the units with clean petrol. Then re assemble. Be careful eg; no naked flames, cigarettes, etc.
A give away if the idle speed control valve is at fault, is that although the engine starts cold, it doesn't raise it's revs much if at all.

Karl Mitchell, Eco-mate technologies ltd
August 2008