My car has bin throwing a p0300 code every once in a while. Has anyone else had this problem. Is it common in our cars? I know the code means it's misfiring. They say check the spark plugs, injectors, and vacum lines, or maybe a o2 sensor.I've checked the plugs and vacum lines, no prob there.

bump

 

My p0300 code was actually caused by a plugged cat.

 

same with my son's car. We replaced the downpipe and no more issues.

 

if i go with a new high flow cat how much louder will it be?