i get multiple cylinder misfire code on 1996 Buick Riviera

checked all plugs, wires and coil packs they are fine, O2 sensors and mass air flow sensor are also new as well as fuel filter. now it is smiking bad from exhaust, and oil drips from mufflers, rough idle revs and stalls

Asked by for the 1996 Buick Riviera
1 answer
possible intake gasket leak, fuel pressure regulator, or ignition module