98 outback help...

[subyL92]

I pulled up these codes on Friday..
P0303 and 304..
Cylinder number 3 and 4 misfire..
But the CEL turns on and off...
On Friday night it turned off let it sit for the weekend
And today (monday morning) the check engine light came on but at 75 it starts flashing AMD wen you slow down to 70mph it quits flashing but stays on..
Pulled up same codes...
Never flashed before...
Has anybody had this problem..
I have a 98 Subaru outback 2.5..
Plz help..

[subyL92]

Also..
Engine is stock with stock headers, running only one cat, and 2.5in piping through apex ..n1 muffler..
And car feels like its running perfect with no hesitation..

[subarunut]

start with the basics if the plugs are close to theyre mileage rating change them same with the wires when you pull them out check the ga on the plugs that could cause a misfire if it still has the problem you might want to look and see if the ignition coil is still good anything that would cause a lack of voltage could be the cause im not completely sure but these are just the basics when you have a misfire if its not noticable