Replaced the following: plugs w/NGK; plug wires; Dist. cap and rotor; coil. I have turned off the check engine light several times with my OBD II scanner, it keeps returning with same fault code. The only difference is an increasing calculation load. I have also changed fuel injector connectors between #3 and #4 cylinders, and spark plugs between same with same fault code. I have not tested EGR, mass air flow, Crankshaft and camshaft sensors, intake leak, or throttle position sensors. I have been replacing one item at a time for several weeks now, and have not found root cause. Please help! Thx!