The nitty gritty is is measures the amount (mass) of the air entering the engine. It uses this information and signals from other sensors like the throttle position sensor, ECT, etc etc, to determine how much fuel to inject at any specific time. If it hasn't turned the check engine light on yet, it will soon. The car will still run because it has the ability to estimate what conditions should be and run off of certain tables or parameters in case a sensor fails or just plain isn't there in your case..
What CAI do you have on there? Is it a homemade thing?