Yeah I have the same scangauge...

And the TECH 2 tool is the $3,500 tool mechanics can plug into your car and get tons of information, reset sensors, ran diagnostics, manually adjust solenoids etc. So they can make sure they're functioning, etc. etc. etc. The CD Manual has full routines for trouble shooting specific issues, and checking if different components are faulty.

We basically guess based on symptoms where the tech 2 can verify the condition of a lot of components without even popping the hood. ie full control over the IAC, they can say adjust to 30% (or whatever) and if it doesn't work, they know it's bad.