I had the head gaskets done on my 09 Impreza. Car runs great but if I floor the gas to get on a highway, the CEL/cruise/traction lights flash and a 0301/0302 code is set. I know this indicates 1&2 misfiring, but i can't feel it. Codes were cleared and stayed off until next foot-to-floor moment. NGK plugs are new. Scratching my head!

If you had the hgs done by a shop. You should be bring it back to them having them look at it.

Because (at least at my shop) when we do HGs we use new plugs and wires etc.

So if there's a misfire that only started happening soon after the job. It's likely related.

 

If you did it yourself. Then swap the plugs and or coils. See if it moves. If not, you'll need to be checking fuel, timing etc.

You need new wires or possibly a coil pack. 

 

GD