[Blue Bowtie]

That "newb" reference was about ME, since I've only been doing this for 30+ years.

As for TBI (and other speed/density MPFI control schemes), the air entering the engine is NOT measured. It is calculated based upon a presumed volumetric efficiency of the engine, throttle angle, engine RPM, manifold pressure/vacuum (MAP), and intake air temperature. The most significant inputs are RPM and throttle angle (thus the term, "Speed") and manifold absolute pressure ("Density"). That usually gets the calculations close enough for any factory stock setup, and the final fuel trimming is done with input from the oxygen sensor. Since the factory spent considerable time determining the correct VE rates for a given engine and building appropriate tables, the systems are usually fairly reliable and work rather well.

The real problems with this type system are that significant variations in pressure don't always get reflected accurately enough in the MAP signal to reflect the true amount of intake air, and any modification which changes the volumetric efficiency (VE) of the engine renders the entire calculation almost useless. Driving from the Nevada desert to Denver can have enough barometric effect to really skew the mixture rich, and the ECM does not have adequate time to integrate BLM data to write new tables. Adding headers, a freer flowing intake, different heads, a different cam profile, altering the air cleaner, and various other changes which can affect VE will throw the whole thing into question. You'll notice that when emissions requirements got more stringent, the MAF reappeared along with a MAP, so that systems could actually measure the intake air mass and trim fuel accordingly and correctly.