Ford 1999 Wagon-Econoline Owner's Manual page 102

Starting
Important ventilating information
If the engine is idling while the vehicle is stopped in an open area for
long periods of time, open the windows at least 2.5 cm (one inch).
Adjust the heating or air conditioning (if equipped) to bring in fresh air.
Improve vehicle ventilation by
keeping all air inlet vents clear of
snow, leaves and other debris.
102