Most modern fuel injected cars use a Mass Air flow (MAF) sensor to determine the air flow rate into the engine and meter fuel according to input from the sensor. The relation between the voltage output of the sensor and mass air flow is adversely affected by a shift to a larger diameter intake tube because the airspeed is reduced. This causes the MAF sensor to ?under report? air flow causing a lean condition at worst and a Check Engine Light at best. To accommodate MAF sensor reporting, many intake systems reduce the diameter of the intake tube near the MAF sensor to stock or near stock size because of the need to maintain the correct air speed for the sensor to report the correct flow rate to the ECU.</p>