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There are a variety of good tutorials already on cleaning the Idle Air Control Valve (IAC Valve or IACV), but most of them focus on the wrong aspects, IMO. So, here's some alternative info in case you're still experiencing erratic idle, light throttle hesitation, grumbly lack of responsiveness, or engine shuddering while on the brakes (most noticeable in Reverse). Many of the symptoms are frequently attributed to the Throttle Position Sensor (TPS) being out of calibration, but when you think about the conditions they occur under -- no throttle or very light throttle -- it makes sense that the IACV would come into play.
I had followed the typical instructions and thoroughly cleaned my IACV twice. Despite being impeccably clean, the intermittent problems persisted... I finally decided last week to clean up one of my spare valves and see if it would work any better.
This guide proved the most informative for understanding what needs cleaning and what doesn't, as well as providing a good visual of how the IACV functions. The key piece for me was realizing how little the cleaning of the shaft and its tip really matters. Yeah, they get gunked up, but the tip has no apparent purpose other than to fill or open up the bypass hole to the intake plenum. Clean or dirty doesn't really matter. The shaft is a bit more important, as it needs to be able to move freely to extend the tip, but I think it's actually the part that screws into the magnet that is significant, not the shaft itself. More on that next.
Following the suggestions in the Planet Soarer guide, combined with tips I found in electronics forums, I used an eraser to clean up the contacts within the black housing, then went over it with QD electronic contact cleaner and a q-tip. I put some anti-seize compound on the shaft, but like stated previously, it doesn't appear that that does anything, as it isn't making contact anywhere. (Edit: Actually, if you spin the magnet/bearing assembly off the shaft, you can depress the shaft/spring and see that it does make contact more than appeared to be the case by just spinning it up and down.) I think the only affect a badly gunked up shaft would have is if it kept the spring that it goes through from functioning, or if it had so much buildup that it can't pass through the opening back into the black housing.
The two, make that three, most significant things I did were:
1) Sprayed WD-40 on and around the two bearings, and worked it in as much as possible. The bearings in my original IACV spun slightly smoother than those in the replacement one I was cleaning up, but both were pretty good. Still, you could feel a bit of that gritty metallic resistance that in theory, could be just enough to throw off the small movements the IACV makes with each electrical signal (the diagnostic procedures will make that clearer). I realize WD-40 is more a cleaner than a lubricant, but either characteristic could be of use here and the bearings were much, much smoother after cleaning up the excess liquid.
2) On all three of my IACVs (don't ask!), I was surprised to see upon closer inspection that the metal half of the housing has the most worthless little plastic o-ring ever. It doesn't fill its space in the channel and is too thin to make contact between the mated surfaces. It's hard plastic, so I doubt it shrunk over time, and it snaps securely in place, so it probably didn't have a softer coating that mysteriously wore away. And all three of mine are identical, so deterioration to that same worthless state is quite unlikely. I picked up a generic o-ring from Ace Hardware that perfectly fit the space and has some actual thickness to fill out the two metal surfaces. (Edit: There's also a similar plastic o-ring between the valve and its black plastic housing. It couldn't hurt to replace it with a better one, but it fills the channel better and actually sticks up above the surface enough to actually do something, so it's probably okay as-is.)
3) Edit: I have a new theory that blows everything above out of the water... As mentioned in post #2 below, the symptoms began to return after 2-3 weeks and steadily got worse. I took the IACV apart again, expecting to feel resistance in the bearings, but it was as smooth as when I put it back together last month. I tried mixing and matching the best parts from my best two assemblies, but I doubt swapping any of the bits would have had any measurable effect.
When I put everything back together, it's back to being silky smooth! So, I'm thinking the IACV itself may not actually be to blame. Instead, my attention is now on the electrical connector. Each time I service the valve, I'm disconnecting and reconnecting the plug. Maybe a firm re-connection is what's actually eliminating the symptoms? The plug faces down and could be affected by gravity and engine vibrations/heat, and the clip on mine is broken as are many people's, so it could be just enough to sporadically lose the signal. Splicing in a new connector wouldn't be much fun... Next time the hesitation returns, I'll have a simple test to do, snugging up the plug. If that solves it, then the solution to this rather major problem of many SCs could be as minor as a zip tie!
That could also explain why Lexus went to a non-serviceable IACV design in '95 or whenever. That's been bugging me... Why make something non-serviceable that shows such a knack for needing servicing? Maybe the need for servicing is actually overstated by the fact that it appears fixed every time the harness is removed and reconnected!
With that done, I've been keeping an eye on it for the past week and am happy to report a 100% elimination of the problems stated in the first paragraph! The SC is a finicky beast, with many fixes ending up being temporary until something adjusts for who knows what. But, this appears to have done the trick. WD-40 on the bearings was probably the most important step -- if you're feeling adventurous, try just replacing the bearings instead of cleaning anything -- but the o-ring may have been allowing some vacuum loss and exacerbating any other issues. My "new" IACV is actually less clean than the original one (some of the residue refused to come off), but it functions infinitely better. Moral of the story: servicing is far more important than cleaning.
the worthless o-ring; barely fills half its channel.
blurry side view of the o-ring that sits below the lip.
This was a concern, originally, as all three of my IACVs were cracked in this same spot. It doesn't seem to matter, however. I guess that part of the housing is sealed off?
I went back to Ace to check the specs on the o-ring I used, for the benefit of those that don't have a spare IACV housing in hand to measure against at the store.
First post edited with o-ring specs for between the two halves of the IACV assembly.
Also, I've had a couple grumbly hiccups return of late. Much less severe than before, but disturbing to have it return after 2-3 weeks of thinking it was completely eliminated. I suspect I'll feel some gritty resistance in the bearings if I take it apart again -- the WD-40 was probably only a temporary fix for that aspect -- so I think I'll go ahead and search for somewhere to buy new bearings to test out that element.
Has anyone managed to find a part number for the IACV's 6-pin electrical connector? There's nothing stamped on it... It's supposedly used on many Toyota products and may even be interchangeable with some TRAC and EGR connectors from what I read. I looked on Drift Motion, where I've had the best luck with random replacement connectors, and didn't find anything. Might be worth inquiring with them, though.
I had the idea today to look at my two spare connectors to see if either had a good clip, and sure enough, one did. Turns out they're pretty easy to de-pin, too. Just take a small jeweller's flat head and press the little plastic tab away from the metal pin, then rotate the screwdriver blade toward the pin to push it out the back. Unfortunately, one of the six plastic tabs broke (typically brittle plastic), so that connector isn't useful, either... At least I now know that it'll be easy to put a new connector on without splicing six wires in that tight space! Just gotta find a fresh, new connector before de-pinning the one on the car.
Edit: Never mind, Drift Motion had it after all (link). I scrolled right past it and then missed it a second time in searching for IAC or "idle air" instead of "idle speed".
Funny, I was expecting $300-350. I got the email notification of your first post and was going to reply, "because it would probably cost as much as a decent used engine!"
I'm stuck with the one on my motor. The screws were stripped when I tried to get mine off in December.
I'm always careful to use the jumbo Philips tip on them because they seem very susceptible to stripping otherwise. If mine ever start to show wear, I'll replace them with hex heads ASAP. Of course, I have two spare sets of the screws... You might be able to get yours out with an extractor set, but I'm not sure how you would line up with the lower one.
Thats wild i'm going to try to peek at mine in the next few days, I am leaning to this being a slight issue for me as well. I get this really long step down in idle when the car is first started. tomorrow is 70* so that should tell me more.
does anyone have the 6 pin connector pin-out spec's so i can resistance test then electrical test my IACM. I just replaced my starter in my 91 LS400 cleaning parts as I go, but now it won't run! It starts, idles very rough and slow, and I can't give it any throttle w/o it dieing. Any help or sugestions would be helpfull. thanks!
Last edited by olddogneed; 04-05-17 at 10:44 AM.
Reason: just read wrong, "can to can't"
any clue what the specs on the screws are? I have bad luck with finding various small screws and bolts. I would like to replace with hex heads but just wanna make sure everything else is proper.
Has anyone purchase one of these? If so where and how much? I believe I'm in need of one if the cleaning doesn't work. Saw one on AutoZone for $700. Ouch!
01-01-15, 12:06 PM
IAC Valve cleaning & maintenance tips
