this is what you need to do.
Take the kick panel off, take the ecu out of the car (undo the 10mm bolt) unplug ecu from harness.
Then plug the ECU back in, when you put it in just tightening up the 10ml bolt is NOT good enough, give the bolt 2 turns then push the plug in on EACH side then repeat this untill the bolt is tight.
Make sure the ECU is pluged in ALL the way and there is no gap. I have seen this happen on countless nissans where people DON"T put the ecu back in properly and they get error codes and engine lights because a sensor does not have a good enough connection.
Try this and let me know how it goes before spending big $$$ on coil packs. Even if it looks like its connected properly, still take it out and put it back in the same i explained.