Possible Causes

WARNING: This page does not describe the selected car, but rather 10 other vehicles, including the 2002 Ford RV Cutaway, 2002 Ford Pickup, 2002 Ford F550 Super Duty, 2002 Ford F450 Super Duty, and 2002 Ford Excursion. However, it is still accessible from the selected car via links, so may be relevant.

Snow, plastic bags or other foreign material may restrict airflow at air inlet.
Misrouted air cleaner ducting.
On engines recently repaired, rags or cap plugs may have been inadvertently left in an air inlet pipe.