Throttle Pos sensor vs. MAP/MAF

[Lamari, Matthew]

In looking at the engine as an air flow circuit, I look at the throttle as 
an impedance, a fairly constant pressure outside, MAP pressure inside, 
another impedance (valves etc.), and a vacuum caused by engine at a certain 
speed.

The thing is, temperature/external pressures aside (which have to be catered 
for anyway even when measuring air pressure/flow),

For a given engine at a given speed, doesn't one throttle position map to 
one pressure?  I understand there can be some lag; but MAP sensors aren't 
instantaneous in reading anyway.

I understand that pressure readings may harken back to the days of vacuum 
advance in old distributors; but, temperatures aside, would a throttle to 
RPM lookup be any different to a Pressure to RPM lookup in any situation?

(I understand existing systems use Throttle pos as a signal of intent, e.g. 
full throttle tells the system to throw extra fuel on top of what it would 
normally in a situation, and low throttle means try to idle; but is the lag 
that significant that, for a given physical setup, one throttle setting for 
one RPM the pressure/airflow changes?

Granted, without this, ducting changes and even a filter change would screw 
things up; but not in a fully calibrating system. . . .


Matthew.