You'll want to start by checking the connection harness to the Mass Air Flow sensor. The MAF sensor is located after the air cleaner and mounted on the air cleaner housing. It is used to measure the amount of air entering the intake manifold. If the unit is defective or the harness disconnect your Infinity's ECU will not be able to determine how much fuel to inject into the combustion chambers.
Check the MAF wiring for loose or disconnected harness, then refer to your vehicle's repair manual for proper voltage testing. It is possible to clean the MAF sensor using Electronic Parts Cleaner (specifically); all other cleaners will damage the MAF.
A new Mass Air Flow sensor for your Infinity I30 will cost around $380.00. replacing the MAF is not difficult and can be done using common auto repair tools. You will need to clear the ECU trouble code (s) after replacing the MAF and drive your Infinity for 100-200 miles in order to complete the "emission monitors".
Your Infinity will be ready for a smog check re-test once all the emission monitors are "READY".