When cleaning won't work and need to place IACV

[OzSir2]

The threads in this forum relate to cleaning IACV to help solve idle problems. When do you determine that no amount of cleaning will work and need to buy a new one? Is there some sort of electronic chip inside the IACV that buggers up? Or is it just a matter of cleaning it enough times until it works eventually?

[AsH_]

i dont think its all to do about the iacv to simply fix idle, many other things like the condition of the hoses from the IACV can be blocked or unable to efficiently flow the coolant.

if you cleaned the iacv you have to make sure the mesh screen is clean, not just a good carby cleaner spray but i tried blowing into the screen to dislodge any bits n pieces still stuck, a air compressor can be good too in addition to the carby cleaner.

check the FITV aswell, clean throttlebody, change coolant or a good flush, it could be the TPS.

i need to change my iacv, i pulled it apart and found lots of corrosion, rust inside and look at the little metal pipes that run off it, they tend to corrode especially if you or someone else has been running water instead of coolant in your radiator system.

i think if the condition of the interior of the iacv is reasonable then there would be no need change it and try to narrow all posibilities down 1st.


everything i have said, i'd like confirmed as i am not an expert on idles.

[EuroDude]

Clean the throttle body and surrounding piping, a dirty throttle body is a very common cause of idle problems in older cars.


If there is an idle problem when the engine is warming up, its the FITV valve that needs screwing in.

If the idle is hunting when the engine is fully warmed up, the IACV filter or throttle body needs cleaning.

[JohnL]

i dont think its all to do about the iacv to simply fix idle, many other things like the condition of the hoses from the IACV can be blocked or unable to efficiently flow the coolant.

i need to change my iacv, i pulled it apart and found lots of corrosion, rust inside and look at the little metal pipes that run off it, they tend to corrode especially if you or someone else has been running water instead of coolant in your radiator system.

In normal operating conditions the coolant has no affect on the function of the IACV. In freezing conditions when the engine and IACV are very cold then the IACV may ice up preventing it from working. The same thing can happen to the throttle body butterfly valve (or butterfly in a carburettor). All the coolant does for these components is assist in warming them up as quickly as possible to help avoid this problem.

If the inside of the IACV is corroded then this is sign of cooling system neglect. If I found corosion in the IACV I'd be thinking about checking the whole cooling system, then flushing it and changing the coolant if I don't know when it was last done, or do know when it was last done and feel guilty / worried about leaving it too long!

[AsH_]

In normal operating conditions the coolant has no affect on the function of the IACV. In freezing conditions when the engine and IACV are very cold then the IACV may ice up preventing it from working. The same thing can happen to the throttle body butterfly valve (or butterfly in a carburettor). All the coolant does for these components is assist in warming them up as quickly as possible to help avoid this problem.

If the inside of the IACV is corroded then this is sign of cooling system neglect. If I found corosion in the IACV I'd be thinking about checking the whole cooling system, then flushing it and changing the coolant if I don't know when it was last done, or do know when it was last done and feel guilty / worried about leaving it too long!

thanks for clearing that up.

good info...

[OzSir2]

So the consensus is there should be no need to buy a new IACV ever??? i.e. you can clean it as well as other associated parts in order to fix problems. But isn't there some sort of sensor inside to which the plug goes to? BTW I have been through other suggested things to do in the forums e.g. very thorough TB clean, clean of FITV, replacement of thermostat, flush of coolant. All this happened quite some time ago...and I eventually took it to a mech who turned the hex screw on the IACV...it cured the hunting idle...but I think it had the effect of disabling its function all together, so at the moment I have been living with very low cold start idle...which I think is leading to problems starting the engine in general.

[JohnL]

OK, going back to your original question, the IACV is a mechanical device in that it has no electronics inside it. It does have a small solenoid inside that is electrically operated by the ECU. This solenoid is quite similar to the solenoid in an injector, and operates a valve that allows air to either pass through or not to pass through the IACV.

This valve is either open or closed or rapidly moving from being open to closed or vice versa. It's never held at a partially open or closed position, the amount of air allowed to pass theough the IACV is controlled by how much time the valve is held open or closed. In practice this means the ECU is causing the valve to open and close in rapid succession, the air flow being metered by 'pulse width' in much the same way as an injector meters fuel.

Whether the IACV needs replacing or not depends upon whether it's actually resposible for your idle speed problem(s). Idle speed problems can be caused by other things, i.e. air leaking into the plenum or manifold from some point, or incorrectly adjusted idle speed in the first place. The FITV may be resposible, but my car doesn't have one and I'm not familiar with them.

If you disconnect the electrical connection to the IACV it should then be in the closed position. Use of AC, lights, window winders etc should then cause a drop in rpm, but just diconnecting the IACV may do this as well. In this case (IACV disconnection causing rpm drop), the base idle speed is set too low and should be adjusted to spec (listed on a sticker on the underside of the bonnet) with IACV still disconnected.

At idle with no auxilliary loads on the engine, the IACV shouldn't have to come into operation, but it will if base idle is too low. This will mean that the IACV will already have used up some of it's capacity just to adjust zero load idle, and when an auxilliary load is placed on the engine (AC etc) the IACV may not have enough capacity left to adequately adjust idle speed resulting in a low idle with auxilliaries in use. It depends on the IACV fitted to your car, some have relatively large ports and can flow quite a bit of air, others have a smaller port opening and can't.

A problem may be that if the IACV is sticking then it may not fully close when disconnected, and will effectively be causing an unwanted air leak causing rpm to be too high, or meaning the idle speed screw (which is just an adjustable air bypass at the butterfly in the throttle body) needs to be closed off too much to achieve a correct idle.

If you remove the IACV and blank of the two exposed IACV ports on the plenum chamber (don't allow anything to get sucked in!, use finger tips firmly pressed to the ports or a blanking gasket under a temporarily refitted IACV), you can set base idle knowing the IACV is not causing a leak. When you refit the IACV, if the idle speed increases appreciably then you have some problem with the IACV. If the idle remains constant, but you still have trouble with rpm dropping when AC etc are used, then the IACV is suspect, and probably stuck shut or partially shut. Leaks associated with the IACV may simply be the rubber seal / gasket (you'll see it when you remove the IACV), or an internal leak that could be just because of gunk, or the unit is faulty.

Don't be too worried about removing the IACV, it's pretty easy and quick. When refitting the IACV, a little smear of non hardening gasket goo on the rubber seal isn't a bad idea. Base idle speed must be set with the engine at full operating temperture.

[OzSir2]

Thanks heaps JohnL for info I haven't seen anywhere else. I know the base idle is out of whack so I'll fix that first and go from there.

[AsH_]

good work...

johnl

[dc2dc2dc2]

my idle was out of whack
cleaned IACV and TB made no diff.
changed the thermostat which fixed the problem!

good luck buddy.

[VTEC@14.7psi]

http://www.superhonda.com/forum/showthread.php?t=259965

Troubleshooting Idle Problems - great info and pics and explanations!

[OzSir2]

Well I set base idle. There is discrepancy between VTEC@14.7psi's link which suggests to set it at 800rpm with IACV disconnected (in my case rpm went up past 1000 when ECU reset and IACV reconnected), whereas the following link
http://www.teirney.net/civic/TipsAndTricks.htm
suggests set it at 650rpm which got me a better result of around 800. I took the IACV off...it looked clean...so not much dirt since I cleaned it ages ago...but the screen NOW has a big hole in it so I will have to get another. And even worse...cold start rpm was about 100 and stalled...so I had to turn the idle screw up (and screw up the base idle) just so I could drive the car. I think the IACV is not functioning at all. I didn't check the FITV this time, but the last time I did I tightened it up according to the diy forums. So cold starts are still a frustrating problem.

[VTEC@14.7psi]

on the link i posted it says the FITV handles cold start so that might be ur problem?

[OzSir2]

Yeah that's right. Perhaps the FITV is stuck in the CLOSED position so it is not allowing any air to go through, thereby not increasing cold idle. This is as opposed to most cases where it will not close...allowing air to go through and cause HIGH idle. I'll have to take it apart and see.

[OzSir2]

OK I think I solved the problem. When I originally took apart the FITV I screwed the thermowax plug all the way in as advised in the forums...turns out it stopped air flow entirely so it worked as if it was always heated up by the hot coolant. So it means that if you have a idle problem, you DO NOT fully tighten the plug...only tighten as much as required (to stop high/hunting idle). I hope this clears things up for people who have the same problem.