IAC indexing and calibration + Difference from OEM to aftermarket....

So having access to three different IAC valves from a 3.4L. I decided to take em apart to see how they work, clean em and hopefully figure out how to index em correctly.

"Oh no only toyota can do that, you shouldn't have taken it apart" guys can exit now...

First the OEM/ Denso valve is original to my 2002 Tacoma's 372k mile motor. It ran my old motor fine but even after a good cleaning or two the truck still had high idle at start up. Would settle down once warmed up.

The second one is a $30 knock off from ebay which NEVER worked out of the box.

The third OEM/ Denso one is currently in my truck and came with a unknown year JDM 3.4L i recently installed. which again has high idle issues.

I decided to take the spare OEM one apart to clean it in carb cleaner chemical dip for 24hrs. After you remove the electronics on one side and the indexed side cap thing/ spring/ plastic jiggy there is basically just a bearing and the shaft left in the assembly. So no plastics or anything that the dip could damage.

After 24hrs in the dip and a can of carb cleaner it came out stupid clean, almost like new. After adding a few drops of some motor oil onto the bearing side and working the shaft back and forth it moves like a couple of midgets covered in oil wrestling in an inflatable pool.

For the electronic side the module just pops back in and tightens down with the two philips screws, simple enough. However with the indexing side it's a different story. Note on the pictures how there is a "capped off" set screw which looks adjustable and by moving it you'd change where the red plastic jiggy stops its sweap. I'm not messing with it but in theory i imagine this would "adjust" something. The outter steel plate with the spring can be indexed and by doing this you slightly change how open/ closed the IAC valve is with no power to it. Inside the red jiggy notice there is a internal slotted area where the nub from the shaft rides. there is also a separate slotted area on the outside where the set screw rides. However i noticed once the electronic side with the magnet is inserted back in, the valve just sorta finds its place 90% closed because of the pull from the magnet. I marked where the outter steel plate with the indexing slots was before taking it apart and have re-assembled it the same. I spent a good hour searching the webs for "How to index/ adjust a toyota 3.4L IAC" and found nothing but cleaning/ testing content. I can't possibly be the first or last to take one apart.

If anyone has the bible factory service manual books and wouldn't mind taking a look at the IAC section and posting up it's contents it would be much apreciated it! i'll be pulling the OEM iac off my truck and doing some side by side multimeter tests to compare the two followed by installing the now stupid clean spare and seeing what it does.

As for the cheap knock off from ebay even though from the outside it looks identical the internal indexing side is completely different. There is NO nub coming off the shaft from which to index anything, no spring and the white (RED on the OEM) plastic part is totally different. Not to mention even though there is a casting boss where the set screw would go, it's not drilled out and there is obviously no set screw. since this part never worked i pulled it apart just to see what the difference from a $300 OEM/ Denso to a $30 ebay one was.













Aftermarket

 

This is a rotary IAC, the details of which can be found here... as far as putting it back together... the ECU learns to control it by guess and check so I'd imagine if you got close to assembled correctly it could probably make it work

https://alflash.com.ua/idlet.htm

 

Have thought the same OP, wonder if it could be adjusted. Searched like you did and found nothing. Looks like the big difference in the OEM and aftermarket pictured is the bi-metal spring. Looks like there would be a couple adjustment points, the stop screw and the spring. My thoughts are maybe the IAC could be slightly adjusted to compensate for slight throttle body wear. It doesn't take much air to jump RPMs 200.

Thanks for the link Speedy.

 

So what is the verdict? I am having the same exact issue with mine. I replace my OEM one with a Amazon $40 one , same problem as the OEM

 

You might need to rule out everything else.....for instance a stuck power steering solenoid would cause a +200rpms....

Couple I've seen the throttle cable just needed to be loosen 1/3 of a turn on that adjustment nut....

what else affects the idle........side pot on TB.....

egr valve and its modulator.....


After studying op's work, most likey these can be cleaned and reused.....
it looks like the spring resets to zero at zero load on solenoid.....
as long as both ends are indexing on that spring......shouldnt wear out...
But gumming up the works.....stressing that solenoid would cause premature failure....and not much there....just the center shaft gets gummed....doubt the spring causes any drag.........maybe the plastic end cap....

With the knockoffs not having that spring......anything could happen.....
you'd be dependent on the cheap solenoid and hard stops on that plastic jig......
wonder if that plastic shaft get sticky over time....

I saved my oem one that came with the truck....I'll take it a part later this spring.....and post what I find.....

 

What do you define as high idle?

 

Maybe check the coolant temperature sensor resistance it might be telling the ECM the engine remains cold hence the valve stays open.

Unless you just forgot to mention that was your first step.

 

Most would say 1000+ on a MT. Not sure on an auto.

 

Bumping this one back to the top. I replaced my IAC 10k ago with and aftermarket unit after flooding out the original when I cleaned my throttle body, assuming it was toast. With the aftermarket IAC I averaged 950-1000rpm at operating temp. I've since cleaned the original and tested it to find it was alive and well. I finally got around to reinstalling the original unit today. It's at 750-800rpm now. Check out the difference in the openings on the OEM (left) and aftermarket (right) below, at least 1/3 wider on aftermarket. That thermal metal spring on the OEM has to make a difference as well. Not exactly sure of how it cycles but darn sure there is a difference in OEM and aftermarket. All OEM for me as a result.



Another difference I noticed when testing either unit on a 12v battery was that the OEM solenoid clicked closed or open with force. The aftermarket sort of swished closed, seemingly way weaker.

 

Developed an occasional slight stumble at low rpm and erratic idle after everything has been replaced with OEM except the TPS. It is a rock auto mid price with only 5k miles on it. So, I set my scan gauge to monitor TPS and the next event showed it sending crazy. Suspected the original OEM IAC I'd cleaned up was weak and thinking it could be flawed in some way, weak or such. Bought new OEM TPS and IAC, installed and idling at 700 rpm consistently at normal op temp. Read it here plenty of times but had to learn for myself, buy OEM if you want it to work right. Maybe this will help someone as stubborn as I am.