2000 Olds Silhouette running rough, flashing Service Engine Light under load. Scan tool gives codes P0101, P0102, P0131, P0137, P0300, P0480, P0742 any suggestions on where to start? I am handy and do a lot of work myself. So far removed and cleaned the MAF sensor, indentified and sealed a vac leak where PCV valve line connects to intake manifold. Bought new O2 sensors and plan on install shortly. Thanks!