What kind of valve cover oil fill "plug" was GM using on the early EFI stuff? Never thought about it before, but an "open" in a valve cover (non-stock breather or bad fill cap seal) will actually affect how your engine runs. Got to thinking about it, realized the later GM stuff is running screw in oil fill caps. Picked a Vortec valve cover set up this weekend due to this. Tested it with my setup, sure enough, engine running, loosen up the oil fill cap, idle change. Trying to wrap my head around this, would the MAP setups have the same problem?