In the morning or when the engine is cold I'm having misfires. This started 3 weeks ago and I changed my plugs 5 months ago with the timing belt. When I crank up my trep it will idle bad but when I step on the gas it will run fine for a min when idling then start running bad. It smokes alot also. When it's at normal operating temp it rans fine and the smoking stops. I pulled some codes that which was P0300, p0303, p0420, and p0430. Think my O2 sensors are causing misfires?