Coming from a lot of great threads that point to the problem that is the Idle Air Control Valve, most fixes revolve around the following found problems:

1. TB Coolant hoses clogged for whatever reason (using green coolant and getting rust, or say the rubber from liquid gasket applied somewhere else, etc.)
2. Air in coolant hoses that were improperly burped during flush or TB reassembly, the cooler air preventing the valve from heating up enough to actually move it (I personally don't understand how this wouldn't self correct if coolant was found to be successfully flowing within the engine, thus eliminating the air in this TB space.)
3. The valve being stuck because of foreign material is preventing it from moving from the default open position; i.e. carb cleaner used and moving carbon from the main TB passageway and finding the lowest point in the IACV route, thus preventing it from closing.
4. The Air Intake Hose being cracked (usually on the posterior side towards the heat of the engine and thus out of our sight line when examining the engine with the hood up,) which allows a vacuum leak before the TB, but after the vain air meter / flow sensor

So let me ask the question that I haven't found anyone else asking:

Should the IACV completely occlude all air from flowing in that passage when closed?

Because my IACV was dirty, it perhaps moves more freely now as its cleaned up, but it certainly does not block all air movement through that passage way. I have tested this off the engine with boiling water. My valve moves successfully, but does not completely occlude the airway when tested with high pressure air, which probably represents the best way to test due to the amount of vacuum any engine of this size normally makes. (Especially include any thoughts on better testing of this.)

In my own testing, I find that in the comparison between cold open and hot closed, the hot closed portion of my trial shows about a quarter of the air movement allowed past the valve. Visually, the valve looks shut with no obvious space between the disk and the lip of the end of its travel. Regardless, air still comes out, and it seems significant enough to cause a higher idle.

Does anyone have any thoughts about this? Should the IACV completely block all movement of air when closed?

If not, why?

If so, it would make total sense to me, but certainly make replacement options killer. Because at this time I don't think it is removable (please confirm/site if it is or it is not. And man have I tried to get it out, sans damage to it that is.)

As I write this I had yet to have re-assembled the TB and place it again on the truck for testing. I will do so this afternoon and report back. This may be all I needed, a good cleaning of the "dry" side of it, when the "wet" (coolant) side was working/flowing successfully as I found it.

I'll add that my TPS was malfunctioning and was replaced. I'm not new to a volt/ohm meter and it was placed correctly, and of course removed before an TB cleaning.

Thanks.

Some previous links I've learned a lot from, but by no means the sum of what I've looked at:
https://www.yotatech.com/forums/f116...le-fix-188519/
https://www.yotatech.com/forums/f116...e-3vze-277269/

For the Google spiders:
1988 Toyota Pickup 3VZE
Throttle Body
TB
High Idle
Idle Air Control Valve
IACV
IAC

 

After cleaning and testing, and after a full flush out of the green AF the the PO left in it, I find that the IACV is still to blame with the tape test (that is putting tape over the inlet IACV passageway before the throttle plate.)

Damn. I guess I'll just JB weld it shut somehow. I've thought about taking the IACV plate off of a junkyard vehicle and somehow engineering a physical choke, actuated by a line into the driver's compartment.

Exams this week so I'll post after brainstorming something up (and heavily researching if it has been done before.)

I don't know that I could trust purchasing a TB out of a junkyard either, merely hoping that the IACV is working in a total part that junkyards around here will probably ask a premium for. Damn they should have made this valve removable earlier in the life cycle of the 3VZE, until the realized the downhill slope of engineering they had put together. (I mean come on, the water pump directly working from the timing belt? WTF. I know Nissan was killing you back in 88, but damn does it seem like a rush on the 3VZE design... /tsk)

 

I'm pretty sure they aren't meant to be air tight when fully closed. Why? They don't need to be. That's what the idle speed adjustment screw is for. As a matter of fact, Toyota states the RPM should drop when the valve is fully closed/engine is hot, and you block the inlet hole. It's not supposed to drop by more than 100 RPM is all. Which means they are never fully closed. See page 8


https://web.archive.org/web/20100114.../forms/h21.pdf


If you haven't figured this out yet...these things don't ever fail. Which is why you're not finding info on how to fix them. And little information on how to even know if one's working correctly. Not too mention no replacement parts. Since why should there be...when nobody needs them? My 88 works just as good as new.


Anyways...I can easily tell you what the problem is. And it ain't the IACV. Odds are some idiot messed with the throttle stop screw thinking that was how to adjust the idle. That's the first thing I'd check. If that ain't it, then you've got air leaking into the intake somewhere. It's just as simple as that.

 

I do really appreciate the post and link to that article, MudHippy, as it was very helpful and precisely the answer I was looking for. So yes, by design the IACV does allow a marginal amount of air to still pass through it, thus the indicated drop of 100 RPM at full OPTEMP on page 8.

Maybe page 8 is the clue to my problem though, as this document shows a finger reaching through to the throttle body to test cover the IACV, implying the obvious that one has to test this with the engine running. In contrast to their shown example, MY engine doesn't even stay running when I pull the air intake hose off, it just dies instantly. I checked the resistance on my VAFM using the Haynes Guide 3VZE numbers, and it was within spec without any precise ability to apply temp variations on test #3, but the correct resistance did measure to its sitting temperature.

Like I mentioned above, I've tried the tape trick twice; differences of trying to find a vacuum leak that wasn't the IACV by having it open and then having it taped closed. (Edit: the tape trick because the engine won't stay running without the air intake from the VAFM. Again, the truck seems to run perfect when the IACV is blocked.)

I do still find myself in the same boat with a high idle, with about six hours today of trying to find it by using carb cleaner and then later by pulling hoses one by which lead the idle to change, and importantly see which don't cause it to change at all, if just to see what would happen. All the 4mm hoses are now silicone, and some of the larger vacuum hoses have been replaced. All to no avail in idle behavior.

Since cleaning the TB when I posted this, I'll note the warm idle is even higher now. Which makes sense as those passageways were stuffed with gunk.

Crank it cold, it idles at 900 RPM, but once it get's to OPTEMP by either letting it sit for a more than a few minutes in this cold weather or by driving it around the block, it idles up to 1400-1500 and begins the famous fuel cut bounce when the brakes are applied for any reason.

I found a youtube of a guy who fixed a 22RE high idle by using sealant tape on the idle screw. I took my idle screw out tonight and found rust on the threads and mud in the channel between the threads and the rubber seal on the screw. I cleaned it up really well and tried the tape myself: no change in idle behavior, but at least it made me feel better knowing it was clean.

That last part is what is also confusing me, another point of me missing something about what the IACV purpose would be if when cold cranking, the truck idles lower than what it eventually warms up to. There are a few tests for some of the temp sensors, so I'll figure I'll give them a go tomorrow. I'll also try to take my AC and Steering out of the loop by capping those off, if just to see what happens too.

 

Great info guys!! My problem persists and I perservere.

https://www.yotatech.com/forums/f116...-issue-293267/

We'll get this together I'm sure.

Let us know your progress Memphis

 

Just a quick note. The engine will (or should) always die immediately when you pull the air intake hose off of the throttle body. A switch in the VAFM opens when no air is flowing, shutting off the fuel pump. This is a safety feature in the event of an accident that kills the engine - wouldn't want the fuel pump to continue pumping fuel under those circumstances. For diagnostic purposes, you can jumper Fp to B+ in the diag connector, and that will keep the fuel pump (and the engine) running even with the air intake hose off.

 

Honda has used a similar style iacv on their engines for a while and they also do not fully close and it is normal. Even the 22re auxiliary air valve has holes in it that do not allow it to fully close. This is all normal.

I know that honda has an adjustable thermo wax plunger inside their iacv that allows for adjustment slightly by turning it in and out. I do not know if toyota has the same or not

 

This is GREAT info RJR. I will try this today!!


ehatch, Thanks for your help.

 

I found your thread and I want to read it again. Very similar, but my own idle problem seams a steady high. I have exams this week but I'll probably get out there today again and try to remove the power steering idle up from the loop. May even cap off the AC idle up too, or try a combination of them both open and closed to see what happens. I've noticed that when I pull the vacuum lines from the plenum to these devices the engine dives a bit, and I wonder if those valves should be freely passing air (until switched) and in fact are not. Especially the PS idle up as the PO sold it to me with the return line not even attached (I say return not really knowing, I only know when I pulled the only existing line then the engine idles down a bit.)

I will try this today, as I like the idea of applying a block and removing it at my own discretion, that way I could better compare sounds between the two instead of the lag in time between removing the air intake hose and applying and then removing tape.

Yesterday, I messed with my new TPS a little more thinking I could lower the .68 idle resistance down to .48, and in doing so I purposefully moved it out of the spec I had it in when I first applied it using the several write-ups found around here (though I had finally used LCE's pdf of this.) I discovered afterwards a surge and a dive in acceleration/de-accerlation with pedal on and pedal off in gear while test driving the few mile loop I test it on. I tested it in and out of this spec with the IACV entry passageway taped and untaped, and essentially found I had the TPS correct the first time.

So I'm back to square 1, leaning towards what Mudhippy has already pointed out, a mystery vacuum leak that I am unable to hear/find by carb cleaner because it may be a bad VSV or switching device on the PS or AC idle up. There seems a few folks that delete the PS pump with a bolt, but I haven't found a consensus on whether one should loop those vacuum attachments or just cap them both. I'm still looking for that answer if anyone has their own thoughts on it. (On that note, my own steering gear is leaking slowly, but I have another ready to go in once I remove its Pitman arm. Steering after three full gas tanks of driving seem to be unaffected, say opposed into comparison of my own neighbor's 86 22R 4x4.)

I discovered this past weekend that the BVSV is not connected because as many have pointed out already, it classically has had its little tubes broken off in the past, therefor my canister is directly attached to the TB by a longer direct vacuum hose. There are several thoughts about this found here, whether one can/should delete it as a temp fix until the plenum is pulled for an easy replacement. It seems like some guys run it open, forgoing the return fumes to assist powering fuel mileage it's argued in helping at OPTEMP, to those who like my own truck, just simply keep it connected by direct line and allowing what is described as a lower idle at cold start up, since one is essentially "flooding" the intake with those extra fuel particles that can choke the idle down during cold start up.

 

Update:

I'm on my second additional throttle body from a salvage yard and still I'm having the same issue where as the truck warms up, the idle speed actually increases from the idle after start (about 950 or 1k,) as though my IACV is opening while I'm driving instead of staying closed.

With the idle screw in all the way, again it starts and runs at about 1k then creeps up to 1200-1400 (it varies with driving, but not quickly,) and it's high enough that I get the fuel cut when applying braking (as mentioned in other threads given high idle.) I've mentioned before, but what stumps me the most, is that when I park the truck for say, running into the grocery store to pick up some things, when I come back out to it and crank it, it barely runs at 400-500 rpm. I believe this is because the IACV is actually closing given the underhood temps cooking it closed by radiant heat alone. This alone is what makes me think it has to have something to do with the IACV, or the coolant somehow doing its job so well that its keeping the valve open because it's not at a high enough temp to close it. I have no clue. I've changed the coolant, and it flows through those hoses when I check them, or so there is fluid in them when I pull them off when the truck is stopped.

olivermeyer posted a reply two months ago in another thread, but I'll include my reply here as well to keep the thread one place I can look back on as I work on it. I may try to replace the o-ring on the throttle screw just for good measure, but given two throttle bodies are doing the same thing, I believe the problem lies somewhere else that I hadn't been able to check much more thoroughly yet. Originally I thought it could be a vacuum issue, and hell still may be, but I've replaced all the hoses with silicone and the seals are tight. I, along with two different shops whom I paid, couldn't seem to find vacuum leaks either using smoke and whatever else tricks they tried, such as I did with carb cleaner and later brake cleaner spraying. I am not dismissing the making of a key that would unscrew that wax seal valve chamber for a much more effective cleaning, but the valves are working in both my TBs when off the truck (boiling water tests) and are obviously having an effect on the truck when it sits and the sitting engine heat soak obviously closes them for rough restarts about 15 minutes later, to then idle back all the way up, by more than a thousand once the coolant starts, I guess, cooling the whole thing down again.

Updates when I can...

 

Pulling the hood off to have the best look I can at those rear coolant temp sensors I can. Maybe the ECU is involved by not getting, or losing the signal that it should be warm when maybe it thinks it isn't... ??? No biggie, it's good maintenance to get behind it best I can and clean it up a little.

 

Wow. It may have been a plugged return coolant line after all. I borrowed a one man brake bleeding kit, which is just a glorified vacuum pump for any old use, and disconnect the coolant return behind the throttle body.

I then used the vacuum to pull fluid from the block supply and the throttle body to make sure it could flow. Check. Then I put the hand pump vacuum on the return side, which would pull the fluid the opposite way from which it would normally return to the Y shape pipe the firewall heater-core return it is shared with. I started pulling fluid and there was a distinctive resistance that was quickly and easily overcome. I figured it might be because I was going the wrong way in the way it was suppose to flow. I got my fluid after only a few pumps but there was a lot of particulates in the coolant. There wasn't a plug, per se, but there certainly was a bit of large black flakes. I took out a half-gallon of fluid this way, which is what it took to get the coolant completely clear of black flakes at any given sample. I primed the coolant as close to the end of the hose as I could and did the same with the TB coolant exit. I attached the two quickly and made sure I replaced the lost coolant on the part of the driveway that slopes 45 degrees, making sure the radiator cap was the highest point, by maybe 4-5 inches at that slope. The radiator fluid didn't seem to move, but I noticed my reservoir was almost completely out, and I was certain it had been topped to the full line. I of course was doing this with the truck running, and it was doing the age old thing on the first crank after trying this; idling at 1000 if just north a bit. The throttle screw had been all the way in this whole time and after a few minutes of running watching the coolant, the truck started to idle down, which it had never done before since I've owned it. It took three full turns of the idle screw to get it back up to 800, and only driving it half a block I had to get out and back out the throttle screw another full turn (putting it at about 4 full turns from bottemed out, what I think I've read as the stock position for the 3VZE.)

Got back home and she was idling at 800 like I had set her on the quick test drive. I'm now cooling it with fans to get it cold again, to test the cold start, and then take it for an extended test drive.

Thanks for letting me vent here, and I do appreciate the help. Mudhippy, thanks again for that document you linked above, man had I been chasing that tail for a while convinced it was that IACV when it wouldn't close all the way, either of the ones on the TBs I had (which led me to really crack down on the coolant/air burb work, again but much better thoroughness this time around, without the distraction of the IACV in my head.)

Test drive after lunch...

 

and now it turns out I did all that without the TPS connected. I left it hanging from when I first started pulling hoses off. Funny too, it ran exactly how I wanted/expected it too with it off. I didn't even think it would run, even at all without it.


hmmmm. Test drive time.

 

It's running like it should now. I rechecked the timing and I'm good there too. I either had air in the TB that I couldn't get rid of without my own use of a hand-pump vacuum, again such as found in those one man brake bleed kits, OR that combined with the black flakes I was pulling from the return coolant line I very well cleared up a flow restriction as the same time.

Well, on to the next thing.