OK, I don't have an L27 to check this on. Maybe one of you guys out there with a good running L27 could verify this. Start up your car- let it idle. Undo the oil filler cap and note any change in the idle speed/quality. Put the palm of your hand over the oil filler hole. Feel any suction? Does the idle change?
I'm gonna go out and try this with my L36. Not the same situation, but similar.
Back in a bit.