2017 Mazda 6 doesn't run properly

[SC Maintenance]

Yes boots always a concern! And if you kinda know what you're looking for you can sometimes spot carbon tracking on the exterior.

Still, absent ANY ignition related codes or misfire counts greater than zero, I wouldn't necessarily chase coils and boots FIRST, esp since OP did a bunch of work just prior.

Torque Pro extended PID's will show misfires for current trip and the average for the last 9 trips - or will on my Nissan's. Its like a $10 app, and you need a $20 dongle. Not sure why more people don't use these great diagnostic tools.

 

[D60]

Torque Pro extended PID's will show misfires for current trip and the average for the last 9 trips - or will on my Nissan's. Its like a $10 app, and you need a $20 dongle. Not sure why more people don't use these great diagnostic tools.

Agreed, and at least on Ford trucks the threshold to actually trip a hard code seems inordinately high. When chasing vague problems it can be nice to see how many misfires are being logged before that threshold is met. It can at least give you a cylinder -- or even a bank -- to scrutinize

 

[Bladecutter]

I did a valve cover gasket, spark plugs, and coils on 2017 Mazda 6. It's the 2.5 liter engine. I then added some B-12 chemtool now I'm getting a troublecode P0421 which idles rough. Can someone help me with this problem please? It been at least two weeks and I just can't seem to get it right. My guess is the oxygen sensor before the cat....

Put the original OEM Mazda coils back on.