WARNING: This page is about a different car, the 2006 Audi A4, 2005 Audi A4, 2004 Audi A4, and 2003 Audi A4. However, it is still accessible from the selected car via links, so may be relevant.
Fig 1: Checking Cylinder Head For Distortion
Courtesy of VOLKSWAGEN UNITED STATES, INC.
Check cylinder head for distortion at several points using knife-edge straightedge and feeler gauge.