I thought I would see what some of you think about this. I figured it was the IACV and it still could be, but I removed it last night and cleaned it with some carb cleaner. The screen looked clear when I removed it and it didn't appear to dirty. My car has had this symptom since I've owned it. That's been about 7-8 years and it just bugs me really.

It'll idle fine most of the time right around 500-600 or so, but sometimes it will drop down to literally 50-100 rpms. It is barely enough to keep it going. This is mostly noticeable and always happens, but not limited to, when I have headlights on or have the break depressed at a stop light or coming to a rolling slow/stop with the clutch in.

Other than this symptom it seems to idle just perfectly. It doesn't bounce around or do anything like that. It warms up great and it won't bounce between 100rpms and 600 rpms, but rather just stay at the excessively low idle speed. If it were ALWAYS at the low idle then I would think that the PO may have turned the IDLE adjustment screw, but since it is a bit intermittent then it leads me to believe that is not the problem.

First off, does this sound like a symptom of the IACV? If so, what additional tests can I try on it? Does the solenoid for it simply work on 12v or is it a lower or graduated voltage to allow it to open in increments? I can definitely test this as well. I'm also curious of the purpose of the coolant that passes through it???


Anyways, thank you for taking the time to look at this and provide any insight. I can check or provide any additional details as well. Just let me know.

 

Usually but not always when it's any kind of idle issue it's vacuum, have you tested to see if it's leaking anywhere?

 

I haven't. I've replaced a lot of the lines a couple years after I got it as general maintenance. I would think there would be some other signs exhibited as well. Everything else runs like a top. I'm definitely open to any suggestions though.

 

Try that

 

 

The only other thing it would seem to me is ground. You can check for ground issues with a dmm, I say that because you both mentioned turning things on that require power...brakes, rolling up windows causing the car to drop in idle. Yes it may be your alternator.

 

 

could be a ground issue, could be the alternator, the ELD, impossible for the IACV because its controlled by the ecu when it kicks on the alternator or the ac compressor.

 

 

 

worn out wires touching somewhere, my wire harness had alot of wires that had cracked casings. check headlight plugs and wires under the dashboard maybe wire wearing out on the pedals .

 

Thanks for all the suggestions. I didn't realize there were posts as honda-tech just now sent me a message saying there were replies. hmmm.....


Anyways, if you read the FSM the alternator does sent a signal to the ECU that is relevant for idle speed adjustment. This could be the problem. I believe my alternator has been "Whining" for several years, but I've personally never heard a confirmed alternator whine nor really cared too much as it just keeps on working. Reading the FSM there are many different idle speeds based on what accessories you have on and none of them are next to 0. haha. It actually increases for the most part as accessories are turned on.

I made a new ground from the head/valve cover to body and from the tranny to either body or frame. I can't recall which it was right now, but it is hooked up as it was from the factory. I haven't looked for other grounds, but I would think I may have some other symptoms if there were ground issues. I did that about 7 yrs ago.

Mine is mostly brakes and headlights that cause it. The stereo doesn't do it. The brakes I would think cause a little load on the engine because of the brake booster utilizing either vacuum or positive pressure to function (not electrical), but if the system isn't compensating for it properly then that would point to IACV (or ECU). The headlights are also suppose to supply signal to the ECU for a bump in idle as well. I believe all of these signals are fed to the IACV essentially to increase/stabilize idle speed.

There's a whole section of things in the FSM that I read about 4-5 days ago and I'm trying to remember it off the top of my head now.

 

i am currently having this exact same issue, did you ever figure it out? I’ve replaced my alternator twice and it hasn’t helped anything. It’s the same exact thing as you, headlights and brakes that causes the rpm drop.

 

This might be the brake booster!

Next time it happens pump the brake a few times and see if the rpms go back up! this used to happen to my 2000 civic.