Diagnosing drivability problems on vehicles, that is.
I handled two today, on my day off... for friend and family. One a mid 90's taurus with a chronic stalling issue, and the other a late 90's pontiac with a lack-of-power issue.
One I solved with a can of carb cleaner and a toothbrush, the other with a TPS and a fuel filter. Neither was a big problem.... as long as you understand how those vehicles are designed.
I had almost forgotten how much I enjoy looking down at a poorly performing engine, and running through myriad possabilities in my mind as symptoms are collated and matched to experience and knowledge. It's a skill developed over many, many years..... and a pleasurable one to use.
Sadly, it's not one that most people are willing to pay for. At least, not what it's worth. A majority of people will happily spend $600 replacing parts on guesswork, and rebel at the idea of $100 for diagnostics and another $100 actually fixing the real problem. Skull sweat too often appears more like magical luck to those who have never done it.
Like the man asked today, "How did you know what to fix?".
I just listened to the car. It was asking for help... I just listened.