Hi my subaru impreza gx sport.when I go to pull off it starts misfiring .soon as I go into 2nd gear it misfires and no power in it could this be the coil pack or something else

It could be coil pack. It could also be spark plugs. When were the plugs last changed?

Vacuum leak can cause them issues aswel

Thanks will try them 

Possible but being a gx I'd hazard a guess at it being less likely an air leak.

Could it be o2 sensor keeps coming up on computer

O2 sensor is a possibility, I've just had to replace one on my Impreza. Mine tended to misfire in a specific rev band, but could be all over. If so, it pays to shop around. Some suppliers want £200-300 for it. Got mine from opie oils for £107, for a denso.
If that isn't the issue, maf could be an outside possibility, or like the others said, coil packs, plugs, maybe an injector. mine benefited from a fuel system clean out with forte my mechanic put through for me.

Sent from my HTC One M9 using Tapatalk

Thank will get o2 sensoe