Check the breather hose to the valve cover? This hose has a small vacuum hose T'd to the lower, hidden part of the aluminum intake manifold.
There is also another small vacuum hose on the underside hidden part of the intake that connects to the fuel pressure regulator at the front top part of the motor.
There is a potential air leak at this underside part of the intake, where a larger hose connects to a switched valve pulling vacuum to the charcoal cannister. This thing never gets attention.
Don't forget to check the hose to the intake from the idle control valve. It is not too fun either.