I have 02 Trailblazer I6 4 X 4 and I am getting misfire codes. I was getting misfire code of p0306 and i replaced a ignition coil. However I am now getting P0300. I was having problems with rough idling and engine lights so i changed the spark plugs first with ac delco iridium. Guess first question is,, how hard on the car is it to drive with random misfire? It doesnt run very bad just when standing still. I was needing to drive somewhere thats about half hour away. Actually, its only when i turn the heater on that it gets really bad. If heater is off its less like to throw SES light. Thoughts?