If your plugs, wires, cap, rotor and a compression test check out okay I would suspect the #3 fuel injector.
It means that more than one cylinder has a misfire history. PO301 would be cylinder number 1 misfire. PO302 would be number 3 cylinder misfire.
It could.
If you have a "check engine" light on, start with having the codes read. A misfire code can tell you which cylinder or cylinders are having problems. A misfire could be the cause of your engine vibration.
Bad plugs, wire , or coil pack.
Bad plug? Bad wire? Bad piston or valve (do a compression test)
sounds like a cylinder misfire..check spark plugs and wires..usually a code will show which cylinder it is, should replace all though
Most likely a bad coil (each cylinder has one) located at the top of each spark plug
Most likely a bad ignition oil. Each cylinder has its own coil mounted at the top of the spark plug
I talked to mechanic and he fixed 5th cylinder misfire on Dodge engine by changing chank shaft postition sensor. It came out on code reader though.
Usually a bad coil , or plug. if the injector was bad , the computer would have coded for it. But the cylinder 3 coil and plug arent that easy to get to. Its the one at the fire wall
P0303 is cylinder #3 misfire. P0300 would be random misfire. Either way you need to diagnose the case of a misfire. Check spark plugs, plug wires(if equipped), cylinder compression, fuel inectors, and wiring.
It could just be a bad spark plug wire or the spark plugs need changing.