A fuel injection engine in a vehicle requires a good air flow to sustain high performance. The air is supplied by the air filter system and the flow though the system is measured by an air mass meter. Volvo performs CFD analysis on the air filter system using a procedure to find pressure loss and flow uniformity index. This thesis presents two CFD procedures designed to improve analysis of these types of systems. The first is dedicated to predicting the flow through the air mass flow sensor present in the system. Experiments show that at low mass flows the air mass meter signal is affected by a noise. Current simulation procedures cannot predict this noise and a new procedure were needed. The procedure developed could not find the signal noise but can be used as a basis for a future transient analysis procedure at Volvo. The second is an optimization procedure designed to find the optimal design for any given geometries in the system with respect to pressure losses and flow uniformity index. The optimization procedure showed promise in finding optimal designs and will be of used in future development. The procedures are tested and developed on existing air filter systems. Experiments were performed with the system in a flow rig and verified the simulated results.