When the Contours underwent a change from a return based to a returnless fuel system, the MAF (mass air flow) sensor housing was changed from an aluminum to a plastic construction for cost savings. However, the two sensors are interchangeable, as previous experiments have showed. Swapping a metal MAF into a newer Contour is not an issue, and often done for polishing/porting reasons. The same can be done in reverse, to gain the weight reduction of a plastic build.