1996 Pickup (22RE) - just developed a tick under load that I originally suspected was an exhaust manifold leak. I could find anything looking. However, while idling I loosened the oil fill cap on the valve cover...as soon as I started to remove the engine RPM dropped and there was enough vacuum under the valve cover that it almost pulled the cap out of my fingers. With cap removed there were mist droplets of oil coming out of the opening. Is this an indicator of an abnormality?