The 1.8's have a valve that maintains air velocity built into the manifold.....when it fails, the manifold requires replacement.Just for kicks and grins, check to see that the oil cap and dipstick are seated properly. I'm not sure what would happen if they were loose, but it's worth checking.
What size engine is this? I thought manifold tuning valves were only on the 1.8.
The 1.4t's have a vacuum check valve built into the manifold....when it sticks closed, the manifold requires replacement.
As the OP has learned, when the check valve sticks, the PCV, more often than not, ends up damaged as well because it has experienced vacuum loads far higher than it was designed for.