A few thoughts.
1. The IAT sensor is located in front of where you’d spray W/M…so the decrease in IAT won’t be read by the PCM/ECM negating any benefit in timing you’d get with a lower IAT. You’d get the benefit of cooler and cleaner combustion with anti-knock properties, but no increase in timing advance that a lower IAT would afford.
2. IF you were to locate the IAT sensor downstream of the W/M nozzle in an effort to benefit from a lower IAT reading, the sensor itself isn’t responsive enough to immediately compensate for an “on demand” lower IAT. So you’d in theory be out of the throttle before the IAT sensor would know what the hell was going on.
3. IF you were able to get lower IAT processed in the PCM as you are spraying, the PCM would add fuel to compensate for a strictly temperature-based denser air charge (cooler air is denser…aka it needs more fuel to maintain a specific AFR at a cooler temp). Latent heat of evaporation gained through W/M injection however actually displaces the air mass available (humid air at temp “X” is less dense than dry air at temp “X”). So all things being equal, your tune would end up being very rich since the engine ‘thinks’ the IAT is cooler, dry air when in fact, its cool extremely humid air which is typically not found in the natural environment.
