Rep Power: 0

2001 Honda Civic EX - 130k miles
Error Code P0505 thrown (doesn't show check engine light since I just manually reset it, but it will come back up).

My car has a surging idle. It does one of a few things semi inconsistently, but the most common is #2, the bouncing idle:
1) Idles fine for a short period of time when cold
2) Surging/bouncing idle from 1200-2000rpm. Bounces up and down.
3) Stable idle at 1500rpm, but very rough feeling. Not quite a knock but the car doesn't seem like it likes it.

Car operates normally above 2k rpm. If below 2k, car throttles itself when clutch is engaged to at least 1500rpm, sometimes as high as 3000rpm, and bounces (2nd part of video).
Exhaust smells really rich.

Super confused what's going on. I've done the following checks:
* Cleaned throttle body
* Replaced IAC valve
* Verified no vacuum leaks
* Performed idle relearn procedure (unplug batt, sit 15 mins, idle with no load for 10 mins - also tried holding 3k rpm until radiator fan spins and letting it idle)

This has been occurring super randomly for about 4 months, but the issue always went away very quickly. Now it occurs every time I drive the car. The car acts perfectly fine if I unplug the battery and plug it back in, but only for a short period of time (about 10-15 mins if I don't touch it and just let it idle. I can trigger the effect by just giving it a little bit of gas though).

Here is a 2 min video of the symptoms:
It seems like its an electrical issue since it doesn't start going ballistic until what I assume is some computer controlled piece activating.
I'm not 100% sure where to go from here. I was tempted to go get a voltmeter and test the TPS today but I wanted to get an expert's opinion before I kept doing more.

Anyway, any help is greatly appreciated. Let me know if you want any more details.

 
Rep Power: 224

To me it looks like the IACV. Did you replace it with OEM or some cheap aftermarket one? I have never seen anyone have any luck with non-OEM IACVs.

 
Rep Power: 0

It was definitely a cheapo 3rd party one.
Specifically, this:
https://www.rockauto.com/en/moreinfo...=1373239&jsn=9

You think I just bought a crappy one and its freaking out?


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Edit: Added content

I still have the OEM one that was actually working smoother than this replacement one. I'll try cleaning it all out really well and installing the original and see if that helps anything.

 
Rep Power: 222

Can also try grabbing one from a junkyard

 
Rep Power: 224

Let's just say I can count on one hand the amount of times I've heard someone have success with non-OEM sensors on these Civics.

You can remove the actual "motor" part of the IACV so you can spin the valve portion by hand. That should help clean it real well.

 
Rep Power: 0

I actually just fixed it this morning. Turns out the aftermarket IACV I bought was a piece of garbage. I cleaned the heck out of the OEM one I originally had and also replaced the electronic load detector (was a $20 fix so figured I'd try it). Drove it 80 miles today. No surge. No CEL. No stuttering or jolting. No idle search. Settles right down to 700-850rpm. All good now!

Beware aftermarket parts. Even if it WAS the ELD, the aftermarket IACV jolted all over the place and acted erratically. I'm starting to think my ELD was bad and the IACV was fine, as we replaced the IACV first and never tried it with the ELD replaced, only with the aftermarket one.

The cleaning of the IACV probably helped too. It didn't appear too dirty (maybe 3-4 q tips of carbon at most), but we're all up and stable now

Thanks for your guys' help!

PS: The OEM IACV has weird pentagon screws so I didn't end up taking the motor off. Just let it soak in some throttle body cleaner and q-tipped it up.

 
Rep Power: 222

Glad you got it figured out 👍