Welcome to the Bonneville Forum!
Please add your year and trim of your vehicle to your signature line. That way when you start asking questions in other areas of the forum, we all have a better idea on how to assist you. Click on "Quick Links" above, go down to "User Control Panel" and then click on "Edit your Signature" It'* pretty straight forward from there.
The P0300 is a random misfire and some issues that cause as well as some solutions are listed here.
You'll have to work through them one at a time until you find the real reason and prevent it'* recurrence.
Please post your continuing saga of repairing this and asking for more help in the 2000-2005 Mechanical section.