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If you take the likely forward velocity range of the car as the air flow velocity into a ram air intake, and convert that to a static pressure, there's not a very big increase in air pressure available.
To alter the air:fuel ratio while running n-alpha (rpm vs throttle position) you want to change the relationship between the throttle position sensor voltage/resistance and the true throttle position. One way to do that might be to add some resistance in parallel or series with the TPS.
In most cases the TPS signal on each engine start is learned by the ECU as the idle value, but if it is outside the expected range there will be a fault code set. Not sure how to work around that and still get the change. Maybe an op-amp circuit? You could map it using an Arduino; true TPS V in, emulated TPS V out. It will probably do some strange things with rapid changes in throttle position too.
The O2 sensor is ignored if the TPS is being used in place of the MAF with a fault code set. The air:fuel mixtures do indeed default to rich as a safety measure.
If you find Autospeed, there are articles there on amplifying an EGR valve position signal so as to increase the quantity of EGR. That may be of value for doing that but also might be used similarly as a method of altering the TPS signal.
It's really easy to monitor O2 sensor voltage with a digital multimeter (volt meter). That will tell you if you're running in open loop. Not so good for tuning though.
Altering the TPS signal will also affect ignition timing.
At low engine speed there is a throttle position beyond which opening the throttle further doesn't increase airflow into the engine. You might want to consider that if altering the TPS signal.
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