thewrai6th

I bought a car with a CEL, P0505. It's having trouble keeping the idle down. It came with a couple rusty IACVs in the trunk, so I guess it was an ongoing problem.
I went through all the troubleshooting in the shop manual.
1. When I plug the hole in the throttle body, the idle did drop, but not very low. I followed the procedure to set the idle to 500 with IACV unplugged and I can't get it to below 1000, even with the idle screw all the way in.
2. I can hear the air getting sucked in when it surges through the throttle body hole. When I unplug the IACV, the idle stops bouncing.
3. I replaced the IACV with a new one from auto parts store, no luck.
4. I bled the coolant twice.
5. Checked the ECU, it's the correct one.
I've built a couple boosted D16Y8s, so I'm familiar with the engine, but this one is giving me trouble. Any advice?

muellersfan

^You have an intake air or vacuum leak.

Fix the problem and then go from there because additional problems may be contributing to the idle issue.

Also, not all 96-00 Civic engines require the IACV unplugged to set the base idle speed. The factory service manual should be your bible when doing car work.

thewrai6th

Thanks what I was thinking, but can't find it. I'll keep looking. The way I see it, with that idle screw all the way in and my finger over the TB hole, the engine should stall or go way below 1000rpm. Butterfly looks clean and sealed. I also checked the play on the throttle cable. Definitely using the Honda shop manual for procedures.

muellersfan

If you don't find a disconnected vacuum hose on the IM, then replace the IM and TB gaskets and torque the nuts and bolts to spec. Then go from there.

Do you have a 99-00 D16Y8 with the FIA system? A leak from that system would throw P0505.

A misadjusted TB cable would not throw P0505.

thewrai6th

Sometimes you just need a gentle nudge in the right direction. Found the leak on the back of the IM, cruise control line was not connected. I found the line connected to... a threaded bolt sticking out of the firewall...gotta love PO hacks.
Thanks again for your assistance!

muellersfan

Nice work!