2013 Cruze LT O2 Sensor question

Thank you for the information and troubleshooting. I placed my finger next to the vent on the valve cover and it had very strong suction. After viewing the threads suggested, I ended up ordering the Dorman set with intake manifold, valve cover and PCV tube for $200. My $200 repair turned into $450 because when I removed the ignition coil, two of the boots broke off at the base. Oh well, my daughter's car got new plugs as well. Replacing everything was relatively easy. I think I spent more time unclipping the sensors and various hoses and harnesses than actually removing and replacing the intake and valve cover. After I was done, I cracked open the diaphragm housing the valve cover and found it hard, brittle and with several tears. Check engine light hadn't come back on again. Thanks again for the help!