A must have 'tool' for a DIYer is a code reader. That is the first thing to do when there is a problem. Though codes are often directional rather than definitive they will certainly narrow down troubleshooting to the core issue. I use the Foxwell 510 elite. 530 is the newer version and you can buy multiple software to cover other brands. The features are the same.
https://www.foxwellstore.com/service...0-scanner.html
Spark plugs don't lie. I would pull a couple of plugs and read them.
https://www.youtube.com/watch?v=lVCs5gWLUyI