Honda Civic engine code issue, here is my.

[P0505] The scan tool indicates Diagnostic Trouble Code (DTC) P0505: Idle control system malfunction.

NOTE: If DTC P1508 or P1509 is stored at the same time as DTC P0505, troubleshoot DTC P1508 or P1509 first, then recheck for DTC P0505.

Possible Cause
IAC valve mechanical malfunction
Throttle body clogged port, improper adjustment
Intake manifold gasket leakage
Intake air hose loose leakage
Vacuum leak
ECT sensor incorrect output

Ok, that is the chart for the 505. It could come down to an idle air control, clogged passage or bad pcm

roy

Follow the chart. It is not a simple repair. You need to follow the chart as we do when we do a diag to get to the real failure. Code numbers never identify bad parts just failed systems

roy