Question

I have a 2003 Ford Focus with code P0304 and P0316, the warning light is ON

Answer 1

P0304 Misfire number 4 cylinder

P0316 Misfire detected on start up

You will need to check the sparkplugs and coil for proper operation  if the vehicle has a coil on plug (COP) look for flash mark that will indicate arcing ignition seeking ground. as well as oil in sparkplug chamber

Answer 2

P0304 FORD Code - Cylinder 4 Misfire Detected
Read more: https://www.autocodes.com/p0304_ford.html

P0316 FORD Code - Misfire Detected On Startup First 1000 Revolutions
Read more: https://www.autocodes.com/p0316_ford.html