mate, sounds electricial - check the connectors for the coil packs to ensure there are no broken wires. with the car running, remove the plug into the coil pack of no.1, it is is worst, than no.1 is fine. repeat through to no.6. when you remove one that makes the motor run no worse - then that is the likely coil pack that is breaking down.
It may not actually be the coli pack, so check all the wiring closely. if it looks good, then put the good coil pack (the newie from Nissan) into that location and see if is still misses on that cyl.
if so, than is it the loom for that plug somewhere. if it fixes that cyl, then it is the coil pack.
let me know.