P0300 Random/Multiple Cylinder Misfire Detected ??? First check???

[longhornsqx4]

Well my Pathfinder has been running like absolute crap upon startup for the last week, sounded like it was bogging/misfiring, well today it finally threw a code

P0300 Random/Multiple Cylinder Misfire Detected

Once the car warms up it runs alot better, smooth anyways and not all choppy like on startup, but my idle seems screwed up aswell, if your at a stoplight sometimes the rpms drop to low and the car stalls.

This all started after I disconnected my battery overnight, connected it in the morning, then this happened.

I have no idea where to start, or what should be possibly checked, diagnosed first.

Any help appreciated, as this car is my bread and butter.

[longhornsqx4]

anybody??