WARNING: This page is about a different car, the 2006 Mercury Mariner and 2006 Ford Escape. However, it is still accessible from the selected car via links, so may be relevant.
Measure the inner diameter of the valve guides in two directions where indicated.
Fig 1: Measuring Valve Guide Inner Diameter
Courtesy of FORD MOTOR CO.
If the valve guide is not within specifications, install a new cylinder head assembly.