98 Millenia Trouble Code P0300

[hipster11]

My 98 Millenia "check engine" light has come on. The code coming up is P0300 (multiple cylinder misfire). What should I be looking for? I replaced the spark plugs recently but all other ignition parts are original. The car has 39,000 miles on it.

[mazdatech177]

if you can pull freeze frame data for the code that was set, check the coolant
temp reading. if it was 70 degrees F or lower id say you have some carbon
buildup on your intake valves. a good top engine de-carbon will take care of it. your local mechanic should be happy to do it for you. if you arent noticing any running problems and you are getting that random misfire code set then its probably carbon buildup. but if you used any other plug other than NGK remove them and use NGK.

[hipster11]

Originally Posted by mazdatech177

if you can pull freeze frame data for the code that was set, check the coolant
temp reading. if it was 70 degrees F or lower id say you have some carbon
buildup on your intake valves. a good top engine de-carbon will take care of it. your local mechanic should be happy to do it for you. if you arent noticing any running problems and you are getting that random misfire code set then its probably carbon buildup. but if you used any other plug other than NGK remove them and use NGK.

Thanks for the response. I was able to pull the freeze frame data. The coolant temperature was 167 degrees. There was another piece of data that came up that may be important. Under Fuel Sys2 it listed OL, fault. I have no idea what that means.

The plugs that I replaced are NGK... the exact same plugs that were in there originally. The only performance problems that I experienced is a slightly rough idle when restarting a warm engine. Once it's running for a minute it smooths out.