WARNING: This page is about a different car, the 2016 Volkswagen Jetta and 2015 Volkswagen Jetta. However, it is still accessible from the selected car via links, so may be relevant.
Courtesy of VOLKSWAGEN GROUP OF AMERICA, INC.
-- Check the cylinder head at several locations for distortion using a Straight Edge - 500mm :VAS6075
and a feeler gauge.