Possible Causes

WARNING: This page is about a different car, the 2008 Ford Pickup, 2008 Ford F550 Super Duty, 2008 Ford F450 Super Duty, and 2008 Ford Cab & Chassis. However, it is still accessible from the selected car via links, so may be relevant.

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