What causes check engine light code #P0506 (idle control system, RPM lower than expected) to display?
If you had the factory shop manual for your 04 Colorado you could open it up & read something similiar to this.
From the factory shop manual for my 02 Hyundai Sonata:
Trouble code P0506 “idle control system RPM lower than expected.”
High resistance between injector fuse and IAC/Idle air control valve.
High resistance between IAC and ECM/computer.
Faulty IAC valve.
Carbon fouled throttle plate.
If this was my Hyundai, i’d start by cleaning items 3 & 4.
You spent thousands on your Colorado, why not spend a few bucks more on the manuals you need to fix it when it breaks???
How many people go out and buy factory/shop manuals? Not that they aren’t great, but does it really warrant 6 question marks? Relax.