Rep Power: 266

I just removed my IAC valve for cleaning, and I notice that in the closed position there is still a big gap at the door, like 1/8 of an inch. Is this normal, or has my spring worn out or something?

I'm still getting a dang Intake Idle system error, and this started after I washed the IAC off with wd-40 and water. I didn't do a very good job cleaning it for some reason.

 
Rep Power: 0

WD-40 should never be used on any car anywhere. Try cleaning it with carb or brake cleaner and see if that helps.

 
Rep Power: 811

yeah carb cleaner ftw. clean it out good, and try not to spray the electronics part, only in the valve. i remember mine was open a bit on top too but cant remember. actually yeah i know it was open cause when i sprayed carb cleaner it leaked down to the bottom.

 
Rep Power: 266

Why?

I used break cleaner and it took it right off. The WD-40 didn't do crap.

We will see if this works...

 
Rep Power: 259

the IAC valve will never be closed completely. It has its own duty of how much air % it allows into the engine. For example on Honda outboards and even Suzuki.. the IAC valves total air % duty is between 15-22%.. so it controls that much air entering the engine at idle.. so yes it will never be completely closed.

and yea wd40 is definately not the thing to used. Its a lubricant, not a cleaner.. well it cleans but thats not its main purpose

 
Rep Power: 266

I don't understand what the point of IAC is for. If I unplug it, RPM goes to like 1500 or so. What would happen if I adjusted idle speed when IAC us unplugged, and started driving with it unplugged? I thought it was the TB's job to regulate air intake even during idle.

Also, what would happen if I unplugged IAC, lowered RPM from ~1500 to about 700, then plugged IAC back in instead of leaving it off as I mentioned before?

I cleaned the IAC real good, and the TB as well. Yes, IAC was very dirty inside. It definitely made a difference. When I let go of the gas, it no longer goes into a state of limbo where it wants to die for 1 second, then RPM shoots back up. Now RPM doesn't drop. I haven't gotten the check engine light yet, but I ain't holdin' my breath.

 
Rep Power: 266

I have a fat key mark on the left side of my car. I don't have any enemies, so I figure it's either because of my Ron Paul sticker, or that long haired middle school kid that I see walking past my car sometimes.

 
Rep Power: 259

The idle air control valve controls the engine idle speed according to the voltage signal from the ECM. The ECM receives input signals from all the engine sensors and determines the correct IAC valve opening which in turn controls the engine idle rpm.. The IAC regulates the amount of air volume allowed into the intake manifold to maintain engine idle speed. At idle the throttle valve closes the intake manifold completely.. meaning all air must pass through the IAC and its bypass passage. The idle adjusting screw that you would use to adjust idle, is actually adjusting how much the IAC valve is opened or closed determing how much air will be allowed to enter the engine at idle.

 
Rep Power: 811

without the iac, the car would die at idle since the TB is closed.

 
Rep Power: 266

No way, it's only partly closed. Air is still being sucked through. That's how RPM is adjusted through the TB idle adjustement screw. The screw opens the TB butterfly. Are you to tell me that the screw should be adjusted so the butterfly is fully closed during idle?

If I'm wrong, then maybe this is the real cause of my idling issues. I haven't gotten an error code yet, but I did mess with the idle a while back, and again today.

 
Rep Power: 811

i guess i shoudve said, the TB plate SHOULD be closed at idle. the iac controls the air intake at idle, not the TB (how can it? the plate doesnt move unless you press the gas). its all electronic. you never should adjust that idle manually.

 
Rep Power: 266

Huh? I'm confused. The idle adjustment screw opens/closes the TB butterfly. I can confirm that for certain because the butterfly moves.

 
Rep Power: 266

You sure about that? Because that implies... well, that idle RPM can't really be adjusted because Idle adjustment screw is only there for setting the butterfly to maximum closure. But if that were the case, why not design the TB butterfly so that it closes perfectly? In it's current design, it has overtravel.

I don't know, are you guys certain of yourselves?

 
Rep Power: 266

I think I understand. If idle were adjusted by TB alone, idle would always vary due to fluctuations in engine temperature and whatever else, right?

 
Rep Power: 266

Nah I disagree, TB should be partially open at idle. The purpose of the TB idle screw is to fine tune RPM. Idle adjustment screw moves the TB butterfly NOT IAC valve mechanism. IAC must be controlled by ECU to keep RPM at +- "X" RPM. The TB is still the primary RPM adjuster. You adjust BASE airflow through TB, then the IAC holds that RPM as engine conditions change. So for example, after I do the 3k rev, I adjust TB screw to say 700. Then it's the IAC's job to maintain that.

Also, I just looked in the shop manual, and it says to rev engine to 3k rpm until fan comes on. Check Idle speed. If out of spec (670+-50) then adjust using idle adjustment screw. Turn on heater fan switch to hi, and AC on for one minute. RPM should be 810+-50.

What I don't understand is why the TB butterfly has overtravel.

 
Rep Power: 811

okay heres what you do. find another throttle body, swap it on, and do the idle learn. problem solved. just make sure its the right one for the transmission you have. $50 on ebay

 
Rep Power: 259

I agree.. you shouldn't be messing with that at all.. and it should rarely ever go out of sync.. its not like you have a carburetor.

Im 100% positive on what the IAC valve is used for. Idle Air Control valve.. If everything is running ok.. then the butterfly valve in your throttle body should be closed off completely. And the IAC controls how much air will flow into and through your intake manifold at IDLE.. thats all it does.. how much air do you think it needs anyway? That little air valve in the IAC does the job just fine and does not need the air of the butterfly valve at idle, to supply enough constant air to the engine.

I know on like.. 2003 and older Honda outboards (which are based off of automotive) have IAC valve adjusting screws.. and idle adjusting screws. But what you adjust to keep the motor running properly is just that IAC screw.. not the idle screw. Its only part of the process, while you're trying to adjust idle for the IAC.. but its not for fine tuning, you back it off of the throttle plate lever so that it doesn't interfere with your IAC tuning, then you put the screw down onto the throttle lever so that its barely touching.. but the IAC is your primary way of adjusting idle speed. Done.

 
Rep Power: 266

So what are you saying, that I should go set TB to closed and let IAC take care of it?

 
Rep Power: 266

I don't need a new TB, the one I have is perfectly fine.

 
Rep Power: 266

I appreciate your opinion, but it's simply not true. IAC with TB closed at idle does not = proper RPM. It doesn't magically put your RPM in spec. IAC revolves around base RPM, which is set through TB idle screw. This guy confirms what I say:

When the car is at idle, the motor controls engine RPM by making small movements to increase and decrease airflow bypassing the throttle plate. The added engine load of an a/c compressor cycling on without the assistance of an IAC movement would cause RPM to drop and possibly stall the car as well. Likewise at part throttle, the IAC motor opens enough to maintain airflow when the TB plate is shut again.

"The throttle plate is designed to allow a small amount of air to slip between the plate and the housing. This maintains a specific amount of airflow that is not designed to change unlike the IAC path."

http://www.dsmtuners.com/forums/arti...operation.html

 
Rep Power: 245

I think you you have your screws mixed up.

If you're turning a screw on the TB and you see the throttle plate move (what you call the butterfly) then you're adjusting the wrong screw. That screw adjusts the travel of the throttle rotor and should not be adjusted.



The idle adjustment screw normally has a plastic cover on it which needs to be removed in order to access the screw. It controls the airflow through the TB via the IACV when the plate is fully closed at idle.

 
Rep Power: 0

Just buy a new car.

 
Rep Power: 266

I'm familiar with where the idle adjust screw is located, and it turns the TB butterfly. I am NOT talking about the base idle screw. The TB butterfly moves whe the idle screw is manipulated. Why would idle adjust pertain to IAC any way? IAC is computer controlled.

 
Rep Power: 266

lol!

 
Rep Power: 266

Nope, you guys are right. Idle screw does NOT move TB butterfly, only base screw does that. Idle screw manipulates IAC air flow. The confusion was entirely my fault, since I had the preconceived idea that idle screw moves TBBF. I was seeing things.

So what now? Should I adjust butterfly using base screw to make it fully closed? What's the best way of doing that?

do you think this was the cause of my idle air control system light? I had it set up so TB was open based off the base screw. Then, I adjusted IAC idle screw to fine tune RPM.

 
Rep Power: 266

So the way I re-adjusted it was, I totally backed off the base screw so that the butterfly bottomed out on the TB itself. Then I adjusted the screw so that it barely pushed the throttle link. The only point of the base screw that I can see is to act as a resting point for the throttle link. If it wasn't there, then the butterfly would bottom out on the aluminum TB every time, which would cause it to dent more and more, especially after peddle is released quickly. So it's a metal-to-metal contact.

Then I adjusted the IAC idle adjustment screw on the TB to 670 RPM.

 
Rep Power: 266

It goes out of sync when things get dirty. IAC has a certain amount of tollerance for dirt --it can adjust-- but sometimes dirt can get so out of hand that it can't compensate. So the first thing to do is clean TB/IAC valve perfectly, then likely it will go back to spec. If not, then adjustments should be made through idle screw while base screw is backed off completely. When desired RPM is acheived, back in the base screw so it just touches, as you said.

Thanks for the help.

 
Rep Power: 245

+1 rep for answering your own posts.

 
Rep Power: 266

Well i'm throwing a code again, bloody hell. That didn't last long. Idle control system. Could it be me 02 sensor? I haven't replaced it.

 
Rep Power: 266

This is what's happening to me:

http://www.hondaforum.com/m_329/mpage_1/key_/tm.htm#510