Anyone with an IAC handy - measurement? (1 Viewer)

[CharlieS]

Hi all,

I'm chasing an idle issue and it might be idle air control (IAC) valve related. Mine wasn't moving, but I disassembled it, cleaned it, and it moves now. What I learned while cleaning it is that the length of the moving part is adjustable.

I made a best guess at installation depth, but am not confident that I got it right.

If you have an IAC uninstalled, would you be wiling to share the depth that the plunger (looks like it may also be called a pintle) is installed?

The doohiickey in the very center of this photo:

I know I should just replace it, but the part is very expensive, even used.

My idle adjusts and is steady in stages while warming up, but when it gets to hot idle it fluctuates dramatically, very low and even stalls. The car catches itself sometimes and revs up. So I think my IAC plunger is moving, allowing more or less air in, but maybe the depth at the mostp closed position (stepped out) isn't right, so the correct amount of air isn't being allowed to bypass the throttle plate?

I know its a long shot, but maybe worth a try?

If I can adjust mine to the proper depth, thats one less variable.

 

[effjay80]

I did a pull-good and replace swap a few years back and my OEM is sitting here on the bench. I measured with my laboratory-grade Harbor Freight calipers from bottom of base to tip of plunger - 59.46mm. Not sure if this is dimension needed or helps?

 

[CharlieS]

Thank you!!!!! Perfect! I really appreciate it.

 

[CharlieS]

Where I had set it by feel:

Lefty loosey (more extended), righty tighty (less extended). It doesn't take very much rotation of the plunger screw when adjusting the depth to make big changes (in hundredths of mm).

Now, corrected to as close as I could get it to match @effjay80 settings:

It might just be in my head, but it seems to idle better (more smoothly) at all stages of cold start and warming up after doing this.

I still have the low idle stumble once hot, but I suspect that is more than likely a vacuum leak...

Thanks again @effjay80!

 

[effjay80]

Was hoping that what you needed. I replaced my IAC along with knock sensors, TPS, VSV/vacuum lines, and a few other parts at same time and idled much better but wasn't sure what was responsible. I like changing one variable at a time better to feel results but as mine is daily driver easier to batch jobs when disabled.

In retrospect I'm sooo happy I tackled lots of these part swaps before the supply chain really started drying up.

 

[CharlieS]

Was hoping that what you needed. I replaced my IAC along with knock sensors, TPS, VSV/vacuum lines, and a few other parts at same time and idled much better but wasn't sure what was responsible. I like changing one variable at a time better to feel results but as mine is daily driver easier to batch jobs when disabled.

In retrospect I'm sooo happy I tackled lots of these part swaps before the supply chain really started drying up.

Yeah, supply down, prices up. Sure is different from when I had my 80s before and parts were readily available and reasonably priced. CDan was my go to back in the day. I miss calling and having him know everything I needed and giving me the mud price. Now I open a browser and hope for the best. Funny how times change. I bet the IAC was a $100 part back then. Now MSRP is astronomical.

 

[CharlieS]

I will say that for me, the prices being higher has me think more about repairing and refurbshing things. When stuff is cheap, it is easy to throw new parts at a problem. Knowing how things work, go together and can be repaired helps a lot when out in the field. I see friends with vehicles that they've never turned a wrench on and rely on professional mechanics, where the solution to being stuck is to call a tow truck and have a credit card handy. I like being one of the guys that can fix his rig trailside, or help a friend do it. I like that kind of self sufficiency. The other thing I find is that some of these systems that seem like a mystery and a black box, are fairly straightforward once you take the time to tear them apart and learn more about them.

Anyhow, @effjay80, you rock and are my hero today. Thanks again!

 

[deckstrom]

@CharlieS, would you happen to remember what the total travel on that IAC? I am bench testing, seem to get only a tenths of a mm movement when applying pos to center terms, neg to either outside set

 

[CharlieS]

Sorry, I didn't think to measure the range of travel, but it was miniscule.

 

[deckstrom]

I am troubleshooting a fast idle issue, would pinching the air supply to the IAC maybe give me clue?

 

[ppc]

I am troubleshooting a fast idle issue, would pinching the air supply to the IAC maybe give me clue?

Your "air supply" are passages within the cast aluminum of the throttle body. Unless you are superman that ain't going to happen. The IAC controls high idle on cold starts which can be as high as 3,000 RPM and lower than idle speed may be as low as 400 RPM in very small movements that may change RPMs by 25 for each step. I would guess the max "throw" of the plunger of the IAC is in the neighborhood of 20mm or more.

Your only choice would be to disconnect the IAC electrical connector and then manually set the plunger position multiple times and testing.

The IAC is a "stepper motor" which you can google to find out how they work

 

[Malleus]

@deckstrom
This is from memory mind you, it's been months since I did this and I didn't record the data: the TOTAL throw of the plunger is about 1/8". If you watch the plunger move as the motor steps, you won't see much, if anything, happening. IIRC, I had to check it three times to make sure it was dead; I was going to toss mine after I cleaned it. On a lark, I measured the extreme positions and finally got the impression it had moved.

I may be wrong about the length of travel, but it isn't much. Certainly not as much as a 1/4".

 

[CharlieS]

@deckstrom I had mine apart again tonight and determined that cycling through grounding pins s1-s4 caused the plunger to move 5 hundredths of a mm per step. I measured it several times and got the same result. So the full range of motion on mine is 0.15 mm. That seems impossibly small, and may well be a failed control valve?

 

[ppc]

@deckstrom I had mine apart again tonight and determined that cycling through grounding pins s1-s4 caused the plunger to move 5 hundredths of a mm per step. I measured it several times and got the same result. So the full range of motion on mine is 0.15 mm. That seems impossibly small, and may well be a failed control valve?

How many times did you go through the full sequence of s1-s4? A 0.15mm measurement implies you only went through the sequence once.

 

[CharlieS]

Around 10 times. I took measurement notes at each step, so I can look at my notes when I'm back home tomorrow. I perhaps incorrectly assumed there were four positions, but maybe this is just a four position step rotation that the ecu fires in the appropriate sequence to drive the plunger in or out as many times as needed to get to the right position? I didn't consider that.

 

[ZackR]

@deckstrom I had mine apart again tonight and determined that cycling through grounding pins s1-s4 caused the plunger to move 5 hundredths of a mm per step. I measured it several times and got the same result. So the full range of motion on mine is 0.15 mm. That seems impossibly small, and may well be a failed control valve?

It definitely moves further than that, a lot more.

 

[ZackR]

Just looked in the 96 FSM and it shows 125 possible positions for the IAC (each step being one). If I recall correctly on mine it moved almost 0.5" from top to bottom.