I was setting the idle and when followed the process I was still getting air thru the IAC TB opening. I put the car in diag, put ignition on, heard the click click, off, then started car (our of diag) and I heard the air whistle and idle is not affected.
So I just disconnected everything and opened the TB and connected the IAC alone. In diag mode I could see it close but as soon as I turned the ignition off it opened about 1/4". Tried with an old IAC and the same thing. Can I have two bad IACs? Is it supposed to do that? This is a TPI TB but the function is the same as a Fiero unit. TIA.

With the ignition off the IAC is suppose to return to it's mechanical set point. If I recall correctly it is suppose to be 1/8" but I am not sure if that is true of all IAC's. I know that some IAC's have instructions on setting the 1/8" opening (Mostly on GM TBI injection systems) and the one I replaced on my original 2.8L did not have an adjustment.

Also once you replace the IAC, The vehicle needs to be drive over 40mph so that the ECM can reset the IAC adjustment. Even if you remove the original IAC and clean out the ports, You are suppose to drive it over 40mph to have it reset itself.
In diagnostic mode it should close so that the idle adjust screw can be adjusted (Sealed on the Fiero TB but some have removed the cover so that they could re-adjust it)

quote Originally posted by Oreif: .... In diagnostic mode it should close so that the idle adjust screw can be adjusted (Sealed on the Fiero TB but some have removed the cover so that they could re-adjust it)

This is the part I'm having trouble with. It closes but doesn't stay like that and air pass by the channel.

I 'think' its ok...in diagnostic mode the pintle is moving to find/calibrate closed position, it may keep making noise while in diagnostic mode forever (in my case). with a running engine it seems it is rarely in the closed position so it may be opened a bit as a default. With the IAC removed from the TB but wired in diagnostic mode it will run even after it shoots the pintle and spring out of sight When taking the fiero over 35mph after startup I usually hear it closing for a split second and then the familiar ssssjjjj comes back....its easy to assume the IAC is bad but if it reacts a bit like the above it does work. Hope this helps, good luck...

What I want to adjust is the base idle. For that the IAC needs to be fully closed (the diag mode sequence to close it), then disconnected, then you adjust the idle screw to base ilde (500-600rpm in my case) then you reconnect everything and move on. My problem is that it doesn't stay closed so I cannot adjust the base idle.

Can you pull the power to the IAC after it closes? (without damaging it of course)

I mean immediately after it closes, before you do anything else.....

[This message has been edited by Hudini (edited 12-08-2006).]

quote Originally posted by Hudini: Can you pull the power to the IAC after it closes? (without damaging it of course) I mean immediately after it closes, before you do anything else.....

Yes, you can pull the plug with the ignition "on", but with the engine not running. In fact, this is the factory method to set the basic idle with the idle screw. Make sure that the throttle body is clean and doesn't have any gunk built up around the edges of the throttle butterfly. That can mess up the idle.

------------------
Rod Schneider, Woodstock, Ga.
"You can't have too many toys!"
1988 Fiero GT
1966 Porsche 911
Van's RV-6 airplane-under construction

Here's a writeup of the process : http://www.thirdgen.org/tpimod2

Does this help some?

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.

How cool. Thank you all I got what was wrong. I thought that shutting ignition off will keep it closed but no. Like you said you need to unplug it while it is being pushed closed for it to stay closed. Thanks all again