Vehicle was presented with misfire. Have swapped coil packs and plugs which makes no difference. When I plug off cylinders 1 and 4 at idle it seems to have less of an effect than cylinders 2 and 3 - which leads me to believe it is a 1 an 4 problem. Do injectors give trouble on these?

Snap on scanner gives codes P0304 and 09474.

Any help appreciated... thanks!