Originally Posted by apkano

The in-car throttle reset procedure only affects the throttle sensor, and drive-by-wire system, making it re-learn your driving habits.

Resetting the PCM wipes any codes set, and wipes out the history the module has learned about engine and powertrain management. It effectively has to re-learn all the sensor inputs. Ignition, fuel, etc. are all reset to the base programming. This WILL NOT wipe out any tunes people have had flashed to their PCM...... it just makes the computer re-learn any adjustments it has made in the past.

Resetting the PCM is strongly recommended if you change over to a CAI as the MAF wil read a totally new reading than it did before, and will speed-up the HP gains the engine attains due to the history stored in the PCM. It's just a law of averages kind of thing...... fuel mileage is easy to increase when you're only averaging it over 20 miles, but much harder to change when you're averaging it over 2000.