Possible Causes

WARNING: This page is about a different car, the 2003 Ford Pickup, 2003 Ford F550 Super Duty, 2003 Ford F450 Super Duty, 2003 Ford Excursion, and 2003 Ford Cab & Chassis. 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.
Tailpipe or muffler may have collapsed or been damaged.