91 300zx Plenum/Vac line leak hiss

[Guinnea]

My ZX has been running really rich for the last few weeks, so I've been trying different things to help fix it. When checking for a Vac Line leak, blowing into the lines, I can hear a hiss coming from the top of the plenum.

Are the lines supposed to be air tight with no air getting through? I've replaced the O rings on it, tried sealing it, and tried soapy water looking for bubbles, and there are no signs of a leak other than the clear sound, and the air escaping when I am blowing into the lines. Is air supposed to be passing through this when the engine is not running?

[ezb57e]

Not sure which line you are referring to, but if it connects to the intake manifold, yeah you might hear the air if you blow on it.
If your car is running rich, a vac leak isn't a likely problem unless maybe the pressure regulator or some other sensor perhaps wasn't getting vacuum.
What is the O2 sensor voltage at hot idle?

[Guinnea]

the one side is reading 0.5V-0.9V. Its not staying very consistent. But the other side is not reading anything. The 12V and Ground are fine, just the white wire is staying at 0.0V. Does the sensor simply need replacing then? I'll keep looking to make sure the connections are fine.
My other thought is the MAF is reading 0.8V with the engine off, and 1.5V - 2.0+V when idling and revving. Is that high?

[ezb57e]

They shouldn't stay steady.
They should switch between about .1V and .9V, especially if you hold the RPM at about 2000.
If the other O2S stays at 0V, that bank is really lean or the sensor is dead, or your not reading the correct wire.
Watch it while you rev the engine a bit, it should rise in response to a rich mixture.
When looking at O2S voltages, low voltages=lean mixtures, high voltages (above .5V) mean rich mixtures.
Your MAF readings sound reasonable.