Yes. Key on, engine off I get 0.66 volts. At idle I get around 2 volts, but it's hard to provide an exact number since the idle doesn't stabilize and the RPMs keep surging. When I first start the car and it's cold and the idle speed is set high by the ECU (1200 to 1500 rpm or so, the MAF voltage is 1.4 to 1.7 volts).

I should have time today and then all weekend to dig into this. Was up until 1am this morning because my brain wouldn't stop grinding away at this. I did a lot of research and I'm really thinking at this point that this has nothing to do with the MAF and instead has something to do with an intake leak. I also have a blow-off valve and I need to check that it is not getting pulled open at idle; it should have the right size spring in it for a typical WRX but with all the changes in the intake/exhaust for the 818, it might need a different spring. I can't fathom where I would have an intake leak since everything seems to be very sealed and secure but I built a pressure tester last night so I'm ready to do an intake pressure test later today.