what's MAF

Mass airflow sensor. It tells the ecu (eletronic conrtol unit) how much air is going to the engine. Along with the O2 sensor, various vacuum inputs, exhaust gas temp (turbo), crank position, H2O temp, ambient air temp, etc, your engine knows how to time ignition & fuel the engine properly. This is how we have driveable 2-300+ hp engines that pass emisions & get reasonable gas milage.