Right out of the book without hooking up diagnostic equipment, the 0300 misfire imay likely be caused by these:

Ignition system failed
Crankshaft pos sensor
A/F ratio
Compression
timing belt skip
EGR system failed

 

I have had the p0300 code for ages. I have had my engine rebuilt with a 2.3l bottom end and still have the p0300. I have had the ECU flashed at the dealer for the p0300 code and still I get p0300. I have had my syncros replaced and my gears inspected to ensure that it wasn't causing extra vibrations. Still I get the p0300!!!

The good news is that with the dealer flash the code is less frequent and I just keep a code puller in my car to make sure it's a p0300 and clear it. I am going to pull my engine damper off and see if that helps but I have been getting them for so long that I doubt it. I just consider it part of my Evo now.

 

Well it seems the reflash doesnt eliminate the problem but does make it less frequent. I used to get it about every 1k miles so hopefully I only get it a few times a year now if I do still get it. Then I'll just buy a Creader to delete it, or if it is only every couple months, just take a quick ride down the street to Autozone and say please...