IAB has a constant loud hiss, idle does not change when I unplug the harness from it.

[rjrobin2002]

I have a mass air efi with a slightly ruff idle. It's IAB has a constant hiss coming from that cap and idle does not change when I unplug it. It's a new IAB when I did the EFI swap. What's up with the hissing and should idle or hissing change when unplugged?

 

[rjrobin2002]

I have all the intake ducted and air filter installed. The hissing is coming from the vent cap on the IAB. It runs great down the road, just kinda idles like it has a cam. I k ow my friends IAB does not hiss like mine is.

 

[DirtDonk]

Hissing is common, but that doesn't make it correct. It is for some, but you're right that most of these don't have any abnormal or bothersome hissing.

Did you adjust the main throttle blade stop screw? Could it be too far open or closed?
If I remember, most of them are only there to keep the throttle blades from closing 100% and then sticking in the bore, but some are also there to set the base idle before the IAC/IAB is connected.
Not sure about all of them, but maybe someone will know.

I'd just be guessing. Not even sure what the "vent cap" is on these actually. Haven't had my hands on one in awhile so can't picture it.
Got a pic of your installation? Which way is the valve oriented? I'm pretty sure that even though they will go on either way, sometimes they don't like a particular way.

Paul

 

[rjrobin2002]

I wish I would of kept the stock one instead of throw it in the trash it when I did my efi swap using mostly new stuff.

 

[rjrobin2002]

It's on correctly, shouldn't the idle change if I unplug it?

 

[ransil]

It's on correctly, shouldn't the idle change if I unplug it?

reset the base isle ( throttle body plate) if idle is not dropping then the plate is open to far.

 

[rjrobin2002]

I will youtube and Google how to do that.

 

[surfer-b]

I wish I would of kept the stock one instead of throw it in the trash it when I did my efi swap using mostly new stuff.

The factory stuff is the only way to go. I tried a new one from parts store, it made a whistling sound at idle, it worked ok but drove me crazy. Take the one you have to a junkyard and pick one from another Ford, most are all the same, the wire plug maybe pointed in diff direction but that's about it. I got one from a 04 Explorer 6 cyl, it worked perfect.

 

[surfer-b]

It's on correctly, shouldn't the idle change if I unplug it?

yes it should, it should drop to the point of almost stalling

 

[rjrobin2002]

I tried my friends IAC and his once installed on mine has a constant hiss with air coming out of this vent on the IAC. My IAC installed on his efi worked fine with no noise.

When I unplugged his IAC while his was idleing, his almost died and idle slowed down.
My idle never changes when I unplug the IAC, then I went through the reset idle procedure and the idle does not slow down when I backed the idle screw out.

What's causing the IAC hiss and the idle to not change when unplugged?

 

[rjrobin2002]

Could I have a vacuum on air plumbing pcv issue?

 

[surfer-b]

Could I have a vacuum on air plumbing pcv issue?

That's what it sounds like. Can you use the filter, MAF and intake hose system set-up, all of it, to the T-body from your friends to see if that's where the prob is?

 

[rjrobin2002]

I could, we are both running all Explorer stuff.
I have plumbed several EFI swaps and have never had this issue.
I am going to pull the upper intake and look underneath to see if something has been kinked or a vacuum cap came off. I am 100% sure the air is sucking or blowing out of the IAC valve cap, just have to find the cause.

 

[EricLar80]

Read the red part:
http://efidynotuning.com/idleair

 

[EFI Guy]

Is it possible you have something causing a bind so the throttle blade is not closing all the way? Have you messed with the throttle stop screw at all?

 

[DirtDonk]

That's what I was thinking too. If you can unscrew the stop to the point that nothing more happens and the engine is still running, then either your throttle blade is not closing all the way or you have a huge vacuum leak!

If the throttle body was ever messed with maybe the blade was not recentered correctly when reinstalled. Never really heard of anyone messing with a TB unit though. Except for maybe a rebuilder.
Is this a junkyard, new or rebuilt throttle body?

Paul

 

[rjrobin2002]

When I backed the screw up the idle never changed, and when I unplug the IAB the idle never changes, but the idle is not high and has no surge. I am just hearing tons of noise coming from the IAB vent cap and have a slightly ruff idle. I can live with its current running condition, just trying to make this hiss noise from the IAB go away and see if it smooths the idle up.

I am going to pull the upper intake and verify my PCV and vacuum plumbing and check the throttle body/throttle cable for that, it is a junk yard throttle body off and Explorer.

 

[rjrobin2002]

Prolly going to unplug the throttle cable and see if it is the problem.

 

[Viperwolf1]

Just an idea here if you can't find the problem. The IAB motor has a diode in it. If the 2 wires going to it are swapped it will not work.

 

[Broncobowsher]

The IAB bolt on 2 different ways. It is common for the IAB to be bolted on backwards. This causes the air to flow the wrong direction. The IAB is direction sensitive. The pressure drop across the IAB may be pulling the valve open instead of pulling it shut (with the solenoid pulling the IAB open to add air for idle)

People often put the IAB on backwards "because it fits better".
There are 3 different styles of IABs as well. So if there is an interference with one you should be able to swap to a different style. http://www.supermotors.net/getfile/231296/fullsize/iac-cutaway.jpg