Codes p0300 p0302 p0442 p0455

[woompa]

My stepmom has a 2000 miata/mx5 and codes p0300 p0302 p0442 p0455 have been coming up. My dad says the car runs very rough only at random times and he says when it happens he has to keep his foot on the gas or it will cut out. I know the 300 code is random misfire, the 302 code is cyl. #2 misfire, the 442 is small emission leak, and the 455 is large emission leak. the 300 and 302 codes i figure are probably a bad coil pack, and the 442 and 455 codes are a bad fuel cap or canister leak maybe? The only problem i have though is that all of these codes came up at the same time and i would hate to pay 250 plus for a new coil if not the problem. Anyone know why these codes showed up at the same time? they have been reset a couple of time only to come back when the car starts to shudder. Thanks for any help