1999 Nissan Quest with misfire on cylinder #1.?

We have a 1999 Nissan Quest at 63K miles with a "Service engine soon" dash-light. The PCM reads "Cyl.1 misfire". Replaced plugs, plug-wires, distributor cap & rotor yeilding a slight improvement, but is still misfiring. Should I replace the the ignition coil(s) and if so where is it?