Honda automatic control valve problem

I have a 1998 Honda Civic (5 speed) that developed a weird problem -- the idle speed would fluctuate every few seconds between low and high, even when the engine was warm. I noticed this during an out-of-town trip and on the way back, the "check engine" light came on. I got a computer diagnostic at a random garage and they say the problem is the automatic (edited) air control valve and that is a $500+ part. With labor and the diagnostic it will be $800+ to get the car fixed--ouch.

Does anyone know what the ACV does, and does the diagnostic make any sense? Is there some hope of being able to somehow fix or unstick the valve instead of replacing it? I'm not averse to attempting a DIY repair, though I don't have access to any serious automotive tools.

I don't drive the car much, so the car has quite low mileage and shouldn't (yet) be experiencing any serious wear-related failures, though maybe some parts become unreliable through just plain aging. One related thing: I was travelling earlier in the year so I had left the car in a parking lot for about 3 months without driving it. The parking lot guys ran the engine once a week which they said was good for it, but now I wonder if that may have had anything to do with the ACV failure. There have been other occasions where I left the car parked for months without running it at all, with no apparent problems resulting.

Thanks for any advice.

I do not know anything about Hondas but my Ford had a IAC(Idle Air Control Valve) go bad whivh caused the engine to idle at 1600 rpm. As they go bad the valve will stick, resulting in different idle speeds. A new IAC valve costs me $60.00 and was dead simple to replace.

I really don't know what an ACV is but if it is the same as an IAC then all it does is change the airflow to the engine to adjust for different loads at idle like air conditioning and headlamps.

Yeah, it sounds like the part in question is the IACV (idle air control valve) and the Honda part is just bloody expensive (online stores have it for around $250, and I guess it's fairly typical for garages to charge 100% markup). I'm trying to figure out how hard it is to get the part off the car and maybe try cleaning it with carb cleaner or something. Also not sure whether replacing the valve will actually fix the problem. Some googling led to the phrase "idle surge" which gets a fair amount of hits and describes some other possible causes. Sigh.

I guess I'll pick up the car then figure out what to do. I have the slight luxury of being able to get around without needing the car for a while.

I would get a cpl cans of carb cleaner and clean the throttle body and the air passage for that valve first then try it out before changing the valve.

Honda makes basic auto maint sound like Minuteman III Warhead disassembly. All REPEAT ALL cars require a throttle body service/cleaning at some time, its exactly the same as a carburator plate/ choke cleaning. All modern cars get gum and varnish in the throttle body over time and it affects idle quality eventually. i'm not saying the valve isn't bad but before I spend $250 i'd like to be sure.

Over the years i've fixed many many customers cars idle problems with a simple toothbrush and carb cleaner in the Throttle body. Remember to let it dry for a few minutes after cleaning it and you may have to feather the gas pedal for a few seconds to clear it once it runs

Does it have a carburator?

Car is fuel injected, no carbeurator I'm pretty sure. I just picked it up at the garage. The guy said he tried cleaning the valve and checked various other possible causes of the problem, e.g. the throttle position sensor, vacuum hoses, etc. and that cleaning the valve didn't help and that the other stuff checked out ok. I do get the impression that he knows what he's doing and that the stuff he tried is consistent with what I saw suggested on some web forums that I googled about similar problems. So the sticking point to me is the $500+ for the replacement valve. I wonder whether a more determined cleaning effort is worth trying. I also wonder whether the car is reaching a point in its lifecycle where stuff is going to start failing all over the place, requiring endless costly repairs. As mentioned I don't use it much these days. So I may be better off getting rid of it, enrolling in a car-share program for when I do occasionally want a car, and buying another car if the day comes again when I need one regularly.

I took the car in to the dealership for an oil change a couple months ago and they wanted to do $800+ of preventive maintenance even though there were no obvious problems with the car. Mainly they wanted to replace the timing belt and water pump based on the car's age, even though it has relatively low miles. I checked the factory recommendations and they really do say to do that, but I decided to defer it til I have more $$$. Anyway I don't have any real bright ideas now.

I used to be a Honda mechanic, I worked on mostly 90s.

$500 is way too much IMHO. Unless that part really costs that much new. It's only like 10 mins labor or 30 mins max to change it out.

The fluctuating idle issue can be caused by two things (well actually three). On the early 90's the idle is controlled by a fast idle thermo valve (for cold start idle) which is usually bolted onto the bottom of the throttle body or on some motors on the intake manifold & only has two or sometimes three coolant hoses. If there's a fast idle thermo valve you will have two holes inside the throttle body, one for the fast idle valve & the other for the air control valve. The fast idle thermo valve wasn't available seperatly for replacement, it came with the throttle body but it's easy to fix this. I won't get into how to fix this though unless you have it.....

Not sure which motor you have but since you have a 98 you might not have a fast idle thermo valve & should only have one hole inside the throttle body for the IAC. On the later 90s they eliminated the fast idle thermo valve & cold start idle was controled by the eacv (electronic air control valve, or also know as IACV (intake air control valve). This usually bolts onto the back of the intake manifold close to the firewall but again depending on what motor you have it may be on the front of the intake manifold.

It should have only two coolant hoses & a green (somtimes gray) two wire plug & bolts on with two 12mm bolts. Unbolt this from the manifold, be careful that you don't loose the figure 8 shaped oring. Coolant will leak from the two hoses when you remove them, I usually stick bolts in them right after I pull them off to plug them. The IAC will have two holes, one should have the mesh screen & the other you will see a gear inside. Clean these holes out with carb cleaner or brake cleaner. This sometimes works but not most of the time it does not. It best to just replace it. If you don't want to buy it new, we usually got them from the junkyard, they usually cost $35 or max $50 (back then).

One way to check if the IAC is functioning, with the motor running, if you unplug the IAC's connector, the idle should drop very low. When you plug it back in the idle should raise back up to normal. However using this method to check will cause the check engine light to come on so if you do not have a method of resetting the light don't do this. IIRC 98 should still be able to reset the check engine light by pulling the ECU & backup fuses.

I mentioned earlier that there could actually be a third method that can cause this. If you are very low on coolant or have an air pocket in you coolant system it can cause the fluctuating idle. An air pocket in your cooling system will cause no coolant going to the IAC & the IAC will think the engine is cold & will cause the cold idle fluctuating. On the late 90s they eliminated the coolant bleeder so if you don't have this (assuming you did have an air pocket) you will have to fill the radiator, drive it around, wait till it cools, then add more coolant and repeat as necessary.

If you need more help with this shoot me a PM or email. I might still have some IACs left in my garage. If you send me a pic of yours & I do happen to have one I'll send it to you (I have no use for Honda parts anymore).

Being a SAAB fanatic, I have had a few issues with Idle Control Valves and for my SAAB, I have found that removing the entire valve and flushing it with carb cleaner works great but do not put anything hard in the valve to help clean it, only use a Q-Tip with the carb cleaner. This may all be irrelevant because Darkzero has pointed out the the Honda IAC is linked to coolant hoses whereas the SAAB is air based but I would check any and all of your vacum lines because I know that at least with a SAAB, any vacum leak will send your idle into a frenzy with the smallest of leaks.

Darkzero, thanks very much for the awesome offer of a spare valve (and the advice). I deeply appreciate it. I was staying at a friend's place when this issue happened, and I ended up taking the car to another garage which my friend recommended. They managed to get hold of one of the valves for $311. Yes the repair cost is almost all from the valve, the labor amount is much lower. This is still a more expensive repair than really seems optimal, but I'll survive it, and it is probably the lowest-hassle way out of the situation.

There are quite a few different versions of the IACV for different models and engine configurations of the car, and the 5 speed one is quite expensive. As mentioned I had found an online discount source of the factory part for $264, so it's unsurprising that full retail (presumably what the first garage quoted) is much higher. The second garage sourced a Delco part and quoted $311 but then later called back and said they got a factory part for the same price, which seems pretty reasonable for a new part under the circumstances. I guess I could imagine trying a bit more persistently to clean the old valve than the garage guys did, but I don't have any car tools these days, and web forums I looked at indicated that the throttle position sensor (behind the IACV, I think) is very delicate, giving me the impression I could damage it if I did something wrong.

Anyway, I'm supposed to pick up the car tomorrow, so except for the semi-whopping credit card bill, hopefully it will all work out.

Thanks again everyone.

Believe me when I say that I damaged an AIC valve once and that is why I know that you need to treat them gingerly.

Back in 2004 I owned a 1996 Civic EX coupe, 5 speed for about 6 months. It had the d16y8 engine and mine also developed the IACV problem you are describing. I remember removing it from the back of the intake manifold and cleaning it out, but I don't think that doing that fixed my problem. I sold the car and let the next owner know about the existing problem (the IACV wasn't my motivation for getting rid of the car). A good place for honda parts is www.hondaautomotiveparts.com

Paulr, let us know how the repair went. :thumbsup:

Next time check www.rockauto.com.

A Delco IAC is showing $106 + ~$20 shipping still less than $150 and should be easy to replace with a ratchet.

I get all my parts there. They based in the US but are one of the few stores that knows how help the customer save on shipping.

Normally the problem also occurs when the iacv is only dirty. so, removing, cleaning + reinstalling it should also be a quick fix.
i also got a '96 honda civic great car i don't know the price for that part, but i think they shouldn't be that expensive. bad for you that most civic's in the us are not manual, correct?

//EDIT: just read that your mate already tried the cleaning...

Thanks for the info about rockauto, it's interesting.

I got the car back yesterday (delay was mostly due to my travelling) and it's fine now, hmm, maybe idling a little bit rough, I'll pay closer attention next time I drive it. I figured maybe the engine computer takes a while to sort itself out after a repair like that. The first garage did try cleaning the IACV but it didn't help.

Overall I think the garage treated me pretty well even I spent somewhat more than I guess I really had to.

Thanks for all the help everyone.

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Actually here is a related issue you guys might have some advice about:

I bought this car new in 1998 and it has rather low miles (about 40k) for a car that old because I've mostly avoided commuting. I had to replace the battery a few years ago and have had the usual scheduled maintenance done at the dealership. This IACV thing is the first real problem the car has developed. However, the garage guy says that all 4 tires are due for replacement. Also Honda recommends replacing the timing belt (an expensive job) after 7 years regardless of mileage. Plus it is probably due for a major service (coolant change etc) due to age. Getting all this done is a fair sized chunk of cash, so what I'm wondering is if the car has reached an age where more and more stuff will be going wrong ($$$$$). I don't drive it very much and maybe the sensible thing for me to do is get rid of the car and buy another one next time I have a job involving commuting. That would save on parking and insurance bills as well as escape from any further problems this car might develop (although, as mentioned, I'm not keen on the level of much higher level of computerization in today's cars vs. 1998). It also occurs to me that I might be getting an insurance discount based on having been continuously insured for 3+ years, so if I went without a car for a while, my rates would go up when I get another one. (I'd use occasional rentals in the interim).

Any thoughts are welcome.

Any form of mass transit available where you live?
Before I retired, my employer offered a free city bus pass. I rode the bus to work and back for over 25 years. No car maintenance, no car insurance, no parking costs= huge yearly savings!

Bicycle, scooter, moped, walking,ride sharing(which you mentioned)-check on CPF green-some great discussions over there! The new electric bikes with lithium batteries look interesting.

Mass transit in my area is good enough (and enough stuff is in walking distance) that I rarely use the car these days. I'm not asking for advice about life without a car--I'm mostly asking for thoughts about whether my current car is likely to need more and more repairs in the near future. I had hoped it would be fairly immune because it has low miles and is a reliable model, but apparently cars get flaky with age even if you don't drive them much.

paulr said:

Mass transit in my area is good enough (and enough stuff is in walking distance) that I rarely use the car these days. I'm not asking for advice about life without a car--I'm mostly asking for thoughts about whether my current car is likely to need more and more repairs in the near future. I had hoped it would be fairly immune because it has low miles and is a reliable model, but apparently cars get flaky with age even if you don't drive them much.

Click to expand...

They're just like people. :laughing:

Yes at over 12 years the car is at the age where more stuff will go wrong. That said there are plenty of cars at over 20 years old. Just keep up the normal maintenance (sometimes even this is more than the car is worth) and learn to do the small jobs yourself.

Like yourself my family has a 12 year old car and many of the expensive repairs are coming up. I picked up a service manual and a decent socket set combined with Rockauto I'm at the point where I know the car better than mechanics do. Some of the jobs are kind of fun to do and you get a rewarding feeling when you're done.

That's cool, I was just offering some options.
One way to play it would be to keep the car until it has another expensive repair. ICE cars do need to be driven periodically. I have a 74 VW beetle that I keep a battery maintenance charger on. Its my back up car that I drive infrequently. It is a simple beast to work on and parts are cheap. So it works well in my situation.

There is something to be said for preventative maintenance. You'll have to decide if you like your current ride enough to put more $$$ into it. If you have a 40-60,000 maintenance, there is still no guarantee that something else won"t break. Of course your alternatives are to buy another used car with lower mileage or a new car-both of which will be even more $$$.