I pulled the hose off of my TB and covered the IAC port with my thumb to see if my car stalled. One thing i noticed, is that the IAC port was making a horrible ear piercing hissing noise. The Car did stall, but i am wondering if that noise is normal. another thing to note is that my idle screw has been messed with because it has not had a plug since i have owned the car.
Are you sure it's from the iac port? Could also be from the Throttle body if the plate is open some from the idle screw.
If it stops when you cover the iac port it could just be because your changing the air flow.
A very small opening in the TB plate can easily make a whistle. Could also be somewhat normal but having the duct on changes the flow enough it stops or you don't hear it.
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05:30 PM
Rodrv6 Member
Posts: 1910 From: Ball Ground, Ga. Registered: Nov 1999
The idle air port can make a lot of noise and that's nothing to worry about. The engine should not quit if you cover the idle air port with the engine warmed up. Either your minimum idle screw has been messed with, and/or the throttle body bore has a layer of gunk on it. Make sure the throttle body bore is clean, especially around the butterfly valve, and with a warm engine plug the idle air passage and adjust the minimum idle screw in until you get an idle at around 700 RPM. Then, unplug the memory power to the ECM for about 30 seconds to clear its memory. Hook it back up and take the car for a drive to let the ECM relearn the idle settings.
------------------ Rod Schneider, Woodstock, Ga. "You can't have too many toys!" 1988 Fiero GT 1966 Porsche 911 Van's RV-6 airplane-under construction
One thing that you need to remember when doing this test is that the ECM will try to make up for you covering the hole... that means it will pull the IAC pintle all the way out while your finger is there. Then when you take your finger away it will hiss like a snake from hell and lessen as the ECM realizes that the air is coming through again. This can cause the car to run lean for a bit and if your IAC is gunky and gets stuck when pulled back it can cause glowing manifolds like a bad vacuum leak. Which it pretty much is, but normally it is a controlled vacuum leak.
And I have to disagree with rodrv6 it certainly should die if you cover the iac port. The Iac should be controlling all idle air. On all the cars I have that are FI (5) the engine will die if I cover the iac port. Messing with the idle screw is a sure way of messing up the idle balance between the tps voltage at idle and the air balance.
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10:03 PM
Fierobsessed Member
Posts: 4782 From: Las Vegas, NV Registered: Dec 2001
If it doesn't hiss loudly when you cold start the car, I'd worry alittle. If it doesn't stall when you cover up the IACV hole, you might have a vacuum leak. Or the throttle plate has been tampered with. I have never seen a 2.8/3.4 not stall with that port blocked. Check your PCV and EGR systems for leaks.
And I have to disagree with rodrv6 it certainly should die if you cover the iac port. The Iac should be controlling all idle air. On all the cars I have that are FI (5) the engine will die if I cover the iac port. Messing with the idle screw is a sure way of messing up the idle balance between the tps voltage at idle and the air balance.
Actually the throttle set screw should be set in a way that it puts the IAC towards the middle of its range of adjustment... the only real way to set the throttle screw is to use something like WinALDL to see the IAC value while you are adjusting it. When you cover the hole usually the engine should drop to about a 500RPM idle, not die. When you uncover the hold the idle will race up until the ECM can recover the IAC... If the IAC has to go wide open just to make the car idle it will be very loud. You can hear what I am talking about by quickly blocking and and unblocking the hole... you will hear the IAC hunting.
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10:47 PM
Denodster Member
Posts: 45 From: Jackson, MI, U.S.A. Registered: Mar 2006
And I have to disagree with rodrv6 it certainly should die if you cover the iac port. The Iac should be controlling all idle air. On all the cars I have that are FI (5) the engine will die if I cover the iac port. Messing with the idle screw is a sure way of messing up the idle balance between the tps voltage at idle and the air balance.
Hmmm..... well, OK, but per my 88 shop manual and AllData, with the idle air controller fully seated (port closed) the idle screw should be adjusted to 500 RPM (700 was incorrect.....) in order to get the proper TPS position. I ran this procedure on my 88 GT trying to solve an erratic idle problem and it didn't seem to help at first until I realized that the inner bore of the throttle body had a layer of gunk on it that was blocking the air gap around the butterfly when it was closed. After I took it off and cleaned it thoroughly I ran the procedure again and had to back the screw out in order to get down to 500 RPM. My idle is rock steady now and has been for the last year or so. Don't know what to say...................... As a matter of trivia, the procedure on my 84 Duke was the same, GM specifies a special tool which is a plug for the idle air passage on the TBI engines.
------------------ Rod Schneider, Woodstock, Ga. "You can't have too many toys!" 1988 Fiero GT 1966 Porsche 911 Van's RV-6 airplane-under construction
[This message has been edited by Rodrv6 (edited 06-14-2006).]
By Skybax: One note , I have done this for a year on one of mine, finally bought a t.b. with the cap still installed , everything works fine now, if you set per factory as I did, you can measure the bottom of the buttery fly to the outer most lip of t.b. and it will be 2 & 1/8th inch. But would still recomend a used or new t.b. with the cap still in it, this method has worked for some folks though, the problem I encountered with it was it would work fine for a day or 2 --then back too the loping 1500rpms back down to 500rpms then back to 1500--well you get the idea.
IAC Set Idle Proceedure::::::::::::::::::::: If everything is working properly, no exhaust leaks, no EGR leaks, and the engine is properly tuned, you can go through the IAC system.
Idle is controled by the IAC valve (idle air control) via the computer and is not adjustable.
You can go over the system if your not happy with where it is idleing. Proper idle for the V6 is roughly 900 RPM.
The set screw in the throttle body is for minimum air flow through the throttle plate which is often misunderstood as the idle screw. Any tweaking of the throttle stop screw will give the ECM fits. The ECM wants to be in control of the idle and is not happy when it can't control it. If the normal learn limits of the ECM are exceeded, they will be reset to nominal, causing an erratic idle.
The IAC and associated passages need to be clean to work right. Remove the IAC carefully. You can clean it (the nipple) using carb cleaner and a small brass brush or rag. At this time also clean the throttle palte. Once clean, install the IAC back in the throttle body and reconnect the IAC wires.
For the ECM to properly control idle, the throttle stop screw must be set for "minimum air". This is a process that sets the idle with the IAC fully extended. To fully extend the IAC, jumper ALDL pins A and B together (just like when you check codes) and turn the key on, but do not start the car. With the key on, not running, and in diags mode, the ECM will keep trying to fully extend the IAC. After 30 seconds or so, pull the IAC connector off the IAC *before* doing anything else. This will capture the IAC fully extended.
Now pull out the jumper in the ALDL, and start the car. Typically the "minimum air" idle speed is in the 500 RPM range. I find the car can bearly run at 550. So as long as you can get it to idle on its own between 600 & 700 your good. Set the idle using the throttle stop screw. (The engine should be fully warm to do this.) Now shut the engine off and reconnect the IAC wires. The ECM does not know where the IAC present position is, so pull the ECM fuse (or disconnect the battery) for 20-30 seconds. (This will cause a complete ECM reset of all learned parameters, including the learned IAC ones. Then reinstall the ECM fuse.
Turn the key on, wait 10 seconds or so, and turn the key back off. This will now reset the IAC to a known key-off "park" position. Now start the car. The engine should idle properly under control of the ECM. There are some learned values, such as an IAC offset for A/C, etc that need to be learned, but this will happen under normal driving conditions. I suggest driving the car right away under all conditions. Stop & go, steady cruising over 45 mph, full throttle, and so on. Pull over a few times and turn the car off, then restart it. The IAC can only learn X amount of counts with each run position. If everything else on the engine is in good condition and operating properly it should be around 900 RPM after coming to a complete stop with slight variations and improve over time.
Mine is almost rock solid at 925 RPM.
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08:32 AM
Denodster Member
Posts: 45 From: Jackson, MI, U.S.A. Registered: Mar 2006
Originally posted by Denodster: I put my finger over the port when the car was hot and it stalled.
If you are talking about the iac little hole at the bottom of the t.b. ---then that would mean you do not have a vacum leak ---or it would keep sucking in air from where the vacum leak would be.
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02:27 AM
Denodster Member
Posts: 45 From: Jackson, MI, U.S.A. Registered: Mar 2006
