My 2003 forester xs issues a p0303 code. It intermittently runs a "little rough" on start up only. I have replaced the plugs and wires. I have checked the primary and 2ndry resistance on the ignition coil, as described by my Haynes manual. The 2ndry is within specs at 12.3K ohms for towers 1-2 and 3-4. Primary resistance does not register btwn 1-2 or 2-4. My questions are, can primary resitance of the ignition coil fail without affecting 2ndry, could some other problem (fuel injector) cause a p0303 code, should I replace the ignition coil?