CEL Codes, where do I turn for repairs?

[FlagstaffSVX]

So I've got these three codes:

24: Bypass air control solenoid valve
28: LH knock sensor
34: EGR solenoid valve inoperable

The powers that be have all said that you should fix the lowest numbered codes first because those systems affect the higher numbered systems. I've found plenty of info on how to clean/fix #28 and #34 but I've only found one thread that had a reference to #24. It's under the throttle body right?

I've got the FSM but it's so big and confusing, I often can't find sections that will help me repair things. The most I found on these codes is a section explaining what they do.

So how do I fix the #24 and are there instructions for translating the U-Check mode codes to the FSM?

Edit: I found the pages in the FSB but it's all rather complicated. I think the part I'm hung up the most on is why do we put sensors on engines to detect problems, when the most common problem is the sensor is faulty? Oh, and the #34 code mysteriously dissappeared as well. Maybe driving through Phoenix at 110 degrees unstuck the solenoid?