Hello and good day:
May I first suggest that you buy a "Haynes Repair Manual" for this Vehicle, this will give you a better Idea of where the IAC is located on you Honda Civic.
An IAC (idle air control) motor is designed to adjust the engine idle RPM speed by opening and closing an air bypass passage inside the throttle body. The car computer or ECM (electronic control module) receives information from various sensors and will output signals to adjust the IAC motor in or out to adjust engine idle speed by controlling engine idle air. An IAC motor can fail one of two ways, either the motor short circuits and stops working or the motor will develop high resistance and cause the IAC control motor to react slowly, either failure will cause the engine to stall at idle. When a trouble code scan is performed it sometimes won't always detect a failed or weak IAC motor. To check the IAC motor remove the unit, with the wires connected turn the key to the "on" position without starting the engine, the IAC should move in or out. If the IAC motor does nothing it has probably failed, replace it with a new unit and recheck system. note: while the IAC motor is removed clean (use aerosol carburetor cleaner) the passages the IAC uses to control idle air speed.
Idle Air Control Valve (appearance will vary)
Please follow these Links:
How Does an Idle Air Control Valve Work? IAC
DIAGNOSTIC TROUBLE CODE (DTC) 0505 IDLE AIR CONTROL VALVE (IACV) CIRCUIT FAULT
Check Engine Light - Lonewolf Online
what is a IAC valve - Google Search
