I have a 98 Accord EX 4cyl VTEC 5sp stick. Had a P0401 EGR valve fault. Found port between EGR and intake plugged with carbon. Had to remove intake cover to clean. Also had to remove IAC valve. Cleaned all parts and surfaces. Reassembled same and started engine. When engine reaches temp and chock is satisfied idle surges between 1100 and 1700 RPM and check engine light come on with a P0505 code. I have removed and replaced the IAC valve a few times with the same results. If I use my finger to plug the vacuum hole in the throttle body to the IAC then it idles smoothly. I can drive it around the neighborhood without a problem. It runs great. But I can't get it through state inspection with check engine code. I've jacked up the front end and burped the coolant line to try and remove any air that I'm told it is sensitive to air in the system.

 

Did you ever figure out what was causing that code I currently find myself in the same exact predicament I have a 1998 Honda accord ex 5speed