Got a CEl the one night, P0505.

I thought I fixed it. Changed the IACV. Found a vacuum leak. Capped everything off. Got rid of a cracked vacuum tank that had no purpose. Relearned the ECU. Burped the coolant.

I got an Innova 3100 obd2 scanner. When I used it, it said I had 2 codes, both P0505. When I clear then, I got a yellow light on the obd2 reader for the emissions saying there's a problem. Once I start driving, the car seems fine. If I park and and turn it off and check the OBD2 reader, i still see a p0505... even with no CEL.

The other day I removed the vacuum tank for cruise control, and capped off the hose that goes to it. I checked my OBD2, no codes, and a green emissions light. I thought I was done... this i got to work and sat in the parking lot in Park, and then my idles gots up and I see that CEL. FML

I still get an idle that slowly goes from 1000 to 1500 and then after a minute of two, drops to 8-900, then gives me a CEL, and a constant ~1500 rpms.

I have searched and searched, asked the jerks on H-T (with very little help or replies).

Am I missing a vacuum hose? i know theres a hose that goes down through the intake mani, but I can't seem to find where it goes.


Car is a 1999 Honda Civic EX with a "D15Y8" and is automatic

Will adjusting the idle screw possibly fix this?

Car does not overheat

 

The hose that goes down through the center of the manifold should go to the PCV valve on the back of the engine block.

Also check for broken FITV on the thermostat housing.

You should try closing down the idle screw. If you take the intake pipe off you will find holes in the side of the throttle body before the throttle plate. These feed air into the engine through various circuits for idling. With all of them blocked the engine should stall out.

 

I used my hand and blocked the TB off completely and the engine stalled.

Some people are saying a small vac leak, bad sensors, and a bad pcv valve. I got a new one today, and 30 ft of the thinner hoses. I replaced all the small hoses and I still got a p0505.

Changing the pcv tomorrow. Also, civics after 98 have a iacv/fitv 2 in one thing. So i dont got a fitv.