skuded

its a 2000 gsr runs great, has a p1456 evap code, when i clear the code automatically the check engine light starts flashing code p0304 and stays flashing until i turn the car off, the car doesnt feel like its misfiring, i just replaced plugs to see if it helped and it didnt change, the ignition side seems like it has strong spark on all cylinders, and fuel pressure is within specs, need to know if anyone has run into this problem