I was personally able to solve a P302, misfire in 2nd cylinder, code by replacing the spark plugs and wires. Worked fine after that. It's generally a very simple ignition problem.
I found on line that the p300 coad is a random missfire in all cylinders and that the last number in a p300 code is the cylinder that is misfiring. Your p302 & p303 would be #2&3 cylinders.
injectors are often the cause of misfire codes on this year and model.
The first thing to try would be new spark plugs plugs and plug wires. This fixes misfires the majority of the time. If that doesn't help check the rotor and fuel injectors.
Either a bad coil or bad fuel injectors. try switching coils with other cylinder and see if code changes. if yes, you got a bad coil, if not, you must change all 4 injectors, cause they will all go bad eventually. I've seen it. I was a Toyota technician.
I have a 2000 Corolla with 140,000 miles that had P0300 and P0302 codes. I fixed it by replacing the original dirty fuel injectors with clean remanufactured injectors. Total cost for swapping injectors was $130. It is easy to do it yourself and the car now runs like it has a new engine.
Easy fix - I can also be water in the gasoline. This is caused by a leak in the underground storage tanks. - If your car was running perfect and you just filled-up and then it starts to run horrible and you get codes P0300 - P0301 - P0302 - P0303 - P0304 this is all cylinders miss-firing. The probability of all injectors getting dirty or all spark plugs going bad at one time is highly unlikely. You should suspect water contamination.
I made a YouTube video on this on February the 24th 2011 - Search YouTube for "water in fuel Toyota obd"