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This is a air/fuel ratio issue. Either the Mass Air Flow is not regiestering the amount of air correctly or the fuel supply is low. (Bad pump or bad fuel pressure regulator).
Since the check engine light is on, the car has already found a fault in the system and stored it as a code. I would suggest that you have the car scanned to find out what the car has found.
This scan typically costs about $90 at most shops. However if you take the car to parts stores, they will do the scan free. Simply ask for an OBDII scan and print out. This will tell you what needs to be reparied/replaced.
P0303 means that cylinder #3 is misfiring. Most likely a bad spark plug, ignition coil, or fuel injector.
In the back of the car right side.
I would start by checking the coil. Remove the coil from cylinder #3 and switch it with coil #5. Then disconnect the battery and wait for the check engine light to come on. When it comes on have it scanned again. If the codes is now P0305 that means cylinder #5 is misfiring. (Bad ignition coil). If the code remains switch the spark plug. See if the code changes. If the codes is P0305, you have a bad spark plug.
Finally if it's not the spark plugs or coil (which I assume it will be ) you will need to switch the fuel injector and see if the code changes.