Try this CCV test when it's hot. If the CCV is stuck, it will suck in extra air and fumes. It is possible the oil drain line was so clogged it couldn't suck vapors. Miss fires and lean codes are also possible with a failed CCV diaphragm. Mine had old miss fires and lean codes. They went away with new plugs and coils. Every now and then, it would record misfires but not set the engine light. Since replacing the CCV system, no misfires or other codes have been present.