This started to occur in Nov of 2016 and stopped after new plugs were put in. Same thing started up again in October of '17 which suggest it is a cooler or cold weather event. Codes are PO301 to 304 + 1399. Additive put in by mechanic produced couple of days relief but light came back on. Suggestions have been put in higher octane gas but that brought no change. The common thread seems to be cold weather. But one wonders!

 

a misfire?. you check to see if its spark related. like checking the wires for oil. if there dry maybe look for problems in coil pack just make sure all the plugs spark good. if it does ok good, look for problems in fuel. for the winter i always use a fuel cleaner with ISO in it. to help remove water from fuel system. gas will not absorb the water it will trap in there so u need "iso heat" or somthing to help burn it off. and 2 treatings of techron fuel cleaner would be nice. walmart has best price on all this. make sure your throttle body is clean too. your cat is probably getting dirty too from driving around missfiring

 

Thanks T Blazer. I will look into the suggestions. Its curious about this. Prior to my arrival in Oct of '16 this car was in San Diego, CA and always garaged. Here in MD it is outdoors. My concerns include engine damage or anytime that the engine would fail and leave me stranded. Any other suggestions are appreciated. I will be talking with my mechanic here and also the one I had in San Diego.