Random misfiring and backfiring

The code is p0300. It began running sluggish. Then day before yesterday when I accelerated going up a hill it backfired and skipped. It has been random but steadily getting worse. I replaced the spark plug wires and removed the distributed cap and rotor and cleaned them as best I could. The screws holding the rotor were rusty indicating moisture (that was this morning). Last night I checked for sparks in the dark. I found very small sparks around a loose bolt that holds a hose strap down to the manifold. I tightened it this morning. I cannot see sparks but nothing else changed.