Service Engine Soon - 97 Lumina

The Service Engine Soon light on my 97 Lumina is coming on. I've found that if the engine is cold and there is moisture in the air, it will run rough after starting (& the SES light will blink) until the car warms up. It then runs fine and the light will turn solid until eventually turning off. Autozone found a code of 300 indicating multiple misfires in cylinders but could not give me any direction for troubleshooting the problem. Any ideas?

Update - Replaced Intake Gasket & fuel injectors

remove the plug wires at the coil paks to see if there is any corrosion. if not check your plug wires for corrosion and high resistence