Sudden high idle and possible fix

[BE4Runner]

So I was on my way to go backpacking this morning, and two hours into the drive I came to my first stop and noticed that my ‘00 V6 auto was idling about 1500 RPM in drive. Pulled into a gas station, and RPMs went up to about 3000 in park. Under the hood I saw a cracked cold intake hose, but a quick check by sealing that with duct tape didn’t seem to change anything. Long story short, I didn’t want to hurt the engine or get stranded, so turned around and drove home.

At home I took out the air intake and throttle body, took off the IAC, and cleaned it all. Honestly it was pretty clean to start with. Also replaced the intake hose. Here’s the part that I’m confused by. The ‘adjustment screw’ on the throttle body, that no one seems to talk about in threads related to this, was backed out almost all the way, causing the butterfly to always sit somewhat open. It could come close to closing if the plunger (throttle opener?) it rests against was depressed, but not fully. (Picture pointing to screw in red and plunger in green below) So I adjusted this screw right until the butterfly was fully closed without depressing the plunger. Put everything back together, and a quick trip around the block everything seems back to normal, idle around 700 in drive, 800 in park.

I can’t seem to find anyone talking about an ‘idle adjustment’ screw on 3rd gens, only older models. Anyone have a clue if I did the right thing here? If so, I’ll take it apart again and threadlock that adjustment screw.

Also, should it be adjusted where the butterfly is closed with that plunger depressed or not depressed (not depressed is how it sits when removed from the truck)?

Thanks for any help.

EDIT: Looks like I'm missing a nut that should hold that screw in place, 20 years/200K miles must have somehow worked it off. Any advice on how to properly adjust that screw is appreciated. Also, I've seen the piece I called 'plunger' referred to as a throttle opener on another thread.

 

[jgue467]

...
causing the butterfly to always sit somewhat open.
... Anyone have a clue if I did the right thing here?

On 00-02s the butterfly s/b slightly open at idle, the idle motor makes final tweeks based on a/c on or not, engine temp. ect.

Luck and enjoy the Runner. :cowboy:

 

[BE4Runner]

On 00-02s the butterfly s/b slightly open at idle, the idle motor makes final tweeks based on a/c on or not, engine temp. ect.

Appreciate the help! I believe the this is true for the 01-02, which have a different throttle body, but the 2000s have the same throttle body as the 96-99. The 01/02 have a motor like you mentioned, looks to me like it spins the butterfly, but the 96-00 have a bolt-on idle air controller that bypasses the butterfly and also some sort of vacuum-driven throttle opener - not totally sure what that piece is responsible for (and that is making it hard to know if I've properly calibrated the set screw!)

 

[mtbtim]

This is interesting. That vacuum connection that the plunger is connected to is for the throttle position function from what I've seen in the factory service manual. Looking through the manual, I didn't see any reference to adjusting the screw you turned. I wonder if this is just something that is set at the factory and not messed with unless I missed the reference to it in the manual.

It sounds like this might have been a total fluke occurrence that the screw backed out.

 

[BE4Runner]

Interesting, I guess so. Hopefully I can set it close enough that the ECU can keep it within a good range.

BTW, thanks for your videos. Lots of help over the last few years, and I used the IAC valve video today for reference.

 

[19963.4lsr5]

Appreciate the help! I believe the this is true for the 01-02, which have a different throttle body, but the 2000s have the same throttle body as the 96-99. The 01/02 have a motor like you mentioned, looks to me like it spins the butterfly, but the 96-00 have a bolt-on idle air controller that bypasses the butterfly and also some sort of vacuum-driven throttle opener - not totally sure what that piece is responsible for (and that is making it hard to know if I've properly calibrated the set screw!)

I have two spare throttle bodies. I’ll put a feeler gauge in them and see what their air gap is. With the exception of my S Series Saturn that throttle stop adjustment was set at the factory and do not touch.

There is really no accurate way to set it on our Toy because the air horn needs connected for it to run. On my Saturn you held your finger over the IAC pypass port and set the throttle stop for 500rpm. Can’t do that with the Toy and it’s use of a MAF sensor.

All three 3.4’s idle at 600rpm in gear fully warmed up. 750rpm in park or neutral.


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[BE4Runner]

There is really no accurate way to set it on our Toy

All three 3.4’s idle at 600rpm in gear fully warmed up. 750rpm in park or neutral.

So if I can get it set ‘close enough’ where it seems to idle about right and feels fine driving, is good enough good enough? Or could it being off affect something else?

 

[19963.4lsr5]

So if I can get it set ‘close enough’ where it seems to idle about right and feels fine driving, is good enough good enough? Or could it being off affect something else?

As long as the IAC can compensate you should be good to go.


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[BE4Runner]

Ok, just want to wrap this one up. I went to a junkyard today and looked at two different 3rd gen throttle bodies. Both of them had this ‘set screw’ on the back of the throttle body adjusted so that the ‘plunger’ (extended because no vacuum applied) was pushing open the butterfly just barely, letting a tiny amount of light around the edges. I grabbed a screw and the nut and drove home to take mine apart again, and set it up this way with some blue Loctite.

I don’t think this ‘plunger’ on the back side of the throttle body has anything to do with a throttle stop or throttle position sensor, because as the throttle opens it almost immediately is beyond the range of the plunger - so the plunger could have no effect when throttle is applied. I also felt for it when the engine was running, and noticed that it retracts a bit (makes sense with a vacuum line hooked up), leaving a gap between itself and the set screw, since the butterfly is stopped by the inner bore of the throttle body from closing any further.

My uneducated guess is that this part is solely to leave a tiny air gap between the butterfly and the throttle body bore when the engine is off, to prevent the two from seizing together. As soon as the engine starts, the ‘plunger’ retracts and no longer interfaces with the set screw (and therefore the position of the throttle), allowing the butterfly to fully close, and then only the IAC can pass air through as needed when the throttle is not pressed. Any merit to this theory?

Interesting side note, I’ve been driving this 4Runner for almost 100K miles without issue, so no idea when or how this happened, but the nut on that screw was missing and the end of the screw itself was actually broken! (Pic below). No clue on the cause, but it does seem to be driving fine and idling in expected ranges for now.

My screw on the left, junkyard screw on the right:

My throttle body with new set screw installed:

Butterfly air gap, hard to get the angle right to show light all the way around:

 

[Dieselchessy]

That set screw looks like it was broken due to poor workmanship. The one screw you can see for the AIC looks wallowed out as well.
Someone’s had that throttle body apart before.

 

[BE4Runner]

That set screw looks like it was broken due to poor workmanship. The one screw you can see for the AIC looks wallowed out as well.
Someone’s had that throttle body apart before.

Good points. I did notice the two stripped screws on the IAC, but was still able to get it off without much fuss. I guess I got lucky that I was able to drive it so long before it acted up.