Hello, H-T!

I'll keep it short: bought a bone stock 5 speed 97 Civic CX hatch and have been going over it replacing stuff before it hits the road.

I have a P0505 code for my IACV that keeps coming back.

Things I've done:
1. New NGK spark plugs appropriately gapped.
2. Cleaned cap and rotor.
3. Valve adjustment.
4. Timing still on point.
5. Tried properly setting idle and it idles smoothly when at operating temp around 750-800 RPM
6. New IACV installed.
7. Bled coolant system using proper procedure.
8. Check IACV plug for any moisture and blew it out with compressed air as well.
9. I have not a single coolant leak anywhere.
10. No vacuum leak anywhere either. I can plug the lower hole in my throttle body and it will stall the motor.

So... I have tried everything I can find right now and the P0505 keeps returning. Sometimes it comes back in 10 minutes, sometimes not until the next day and I drive a lot.

The car idles perfect from cold to warm and there is no sign of surging or any improper behavior at all.

I have no idea why the code keeps returning but my idle surges when the MIL is illuminated and returns to normal when I erase it.

HELP!!! I HAVE TO CARRY MY DAMN SCANNER WITH ME TO KEEP ERASING IT!!

 

Bump.

Updated first post some but still need help.

 

Check the wiring and the actual plug to the IACV. Could be just a bad connection.

 

Any other symptoms besides CEL? High/surging idle? Mine was throwing a p1509 iacv circuit failure. The cause turned out to be a poor connection at the ECU. Like you, I had tried everything and was at my wit's end. Try unbolting your ECU, unplug it and visually inspect harness for loose wires/pins. Then plug ECU back into the harness and try starting the engine and clearing the code. Fixed mine..