OBD2 codes in my experience are about as good as poking around the engine bay in many cases. Something many people don't suggest is If you already have a laptop and a few bucks get a cable and software that can poll OBD2 sensor data. The factory...

Adding to "anything rubber" inspect anything that rubber hoses connect to as those surfaces could probably use some TLC (the aluminum thermostat housing comes to mind). Pitting on these surfaces can go deeper than it would at first appear and...