Unless you're overseas (and I'm not even sure about that) your car is a 300SE, not SEL. The 300 wasn't available in a long-wheelbase here in the US in '92. I've got one myself.

The mass airflow sensor is the tube that sits atop the electronic throttle actuator under the air cleaner. It's black, about 3" in diameter and 4 or so inches long.

I believe it does have limp-home mode, and I'm sure it does store trouble codes. By the passenger side hood hinge you'll see a rectangular black cover with a round cap at the forward-most edge. Beneath that cap is the X11 (I think that's the number) connector where you can pull DTC's for all of the car's various systems. I believe DTC's for a faulty mass airflow sensor would be stored in the LH module.

You can build your own (or purchase from various sources on e-bay) a impulse counter tool to allow you to pull your own codes. There are 3 wires, one for 12v+, one for ground and one that plugs into the proper port for the system you want to pull codes for. It's easy as pie to pull codes - suggest a membership to AllDataDIY.COM for $20/year to give you access to all the codes these beasties can throw.