Q: Car stalling at average speeds, no engine codes

A faulty air mass meter could cause drivability issues and not throw a code right away. The air mass meter is one of the sensors that help sets base injection timing. If the sensor is reading correctly but is within the parameters of the the engine control unit, it may not set a code, and then can lean out the engine on slow down from a steady cruise and starve the engine of fuel by cutting injection timing back too much.

Looking at the oxygen sensor voltage while slowing down from a steady cruise could indicate what the oxygen sensor is seeing while decelerating. You may want to enlist the help of a mechanic, such as one from YourMechanic, who will have the diagnostic equipment and expertise to track down the source of your stalling issue.