P0300

I have a 08 Mazdaspeed 3 and I can not begin to understand what is wrong. The code is for random misfire. Has anyone else been able to figure this one out. I changed my spark plugs over to ngk plugs and would not let me start my and put it into limp mode. I put my old spark plugs back in and it started right back up. The gap was set to the spec for the car. I'm thinking I need to change my coils but I'm just seeing what you guys think. Mazda wouldn't tell me anything. And before I go out spend 300$ on new coils. I would just like to know what you've guys done to fix this problem. Thank you!

 

I switched back to regular stock heat range. I had 1 step colder plugs and on cold starts the engine would have very rough idle and spit out a po300 code every once in a while. What I learned from the other forum was that it could be either:

• Coils
• Maf sensor
• Vacuum leak
• CDPF/ spill valve
• fuel rail valve
• purge control solenoid
• PCV valve could be stuck
• EGR valve stuck open
• VVT malfunction.

I'm not an expert, but hope this helps, because it helped me.

 

I found out that my plugs were not gapped properly. Got ngks in now and works a lot better.

 

Good thing it was an easy fix

 

I was getting the p0300 code as well at start up on cold starts. One thing that helped me was to turn car to "on" for like 15 seconds before starting up.

 

Do you know the reasoning for this?

 

Primes everything before start up maybe, tuna suggested it. I also cleaned my throttle body and maf sensor before thinking that was the issue, but just yesterday morning I went to leave and just started it and got the code. Im using step colder plugs too might switch back to stock range like you and see what happens.

 

Make sure you verify plug gap.

 

Indeed

 

Just in case this came back for you....
https://mazdaspeeds.org/index.php?threads/p0301-and-p0300-solution.5928/