I'm getting a code 35, and surging idle. I have a bin at the shop with a bunch of used IAC valves.

Do I just simply swap one out for another and see if the code goes away?I remember long time ago with my 2.5 I was reading that you have to reset the IAC valve, is that true with the 2.8? Is there a way to check the functionality fo the IAC valve before installing it?

There's an IAC reset procedure, search on here will probably find it, can't recall it offhand.

Only way I can think to test on is put a voltage on one terminal, ground the other and read the voltage from the wiper terminal as you turn the shaft, should increase and decrease steadily with no dead spots. Any jumps or dead spots would indicate it's no good.

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Dave

www.ltlfrari.com

Ah - no that's not how the IAC works. You're thinking maybe the TPS.

The IAC needs to have it's pintle inserted into the valve far enough so it doesn't bottom when installing.

After installing, reconnect the battery. Take it out for a drive and be at over 35 mph and the ECM will seat the IAC. That is all that is needed for the ECM to learn it.

[This message has been edited by phonedawgz (edited 07-20-2010).]

is there a "Ohm Test"? I would assume, being just a coil/solenoid there would be a at least an Ohm check or continuity check?

From the SM:

Check resistance across IAC coils. Should be more than 20 ohms between terminals opposite harness connector terminals "A" to "B" and "C" to "D".

Pull the air cleaner to TBI snorkle ,,eyeball inside theTBI ..if the area around the throttle plate is dirty ,wipe it ,,use carb or brake cleaner,then clean IAC by spraying inside the small hole you will see where the IAC is,,if the engine runs better then pull IAC gently clean rubber or metal tip use Q-tips and clean IAC mounting area ,,do NOT ajust this unit unless you know what you are doing..
..make sure you do not have a vacuum leak in the EGR area
careful removing this unit with a wrench easy to damage,, socket prefered

[This message has been edited by uhlanstan (edited 07-20-2010).]

quote Originally posted by phonedawgz: Ah - no that's not how the IAC works. You're thinking maybe the TPS.

Oops, yes you are right...

FYI, shorting the diagnostic terminals and turning the key to the "on" position will also re-seat the IAC valve. When you do that, leave the key in the "on" position for a few seconds to let the IAC valve do its thing.

Checking the resistance of the coils - can tell you if yours is bad, but it won't tell you if it is good. One of the things you can do, if you are so inclined, it to take the IAC out of the throttle body but still have the connecter plugged to it. Now stick your finger into the IAC hole and hold the IAC in the other. Sticking your finger tighter into the hole will 'adjust' the engine to idle slower. Pulling your finger out will make it run faster. The ECM will try to adjust the idle with the IAC in your hand. You should be able to make the ECM run the pintle in and out. Watch out - let the idle stay too high too long and the IAC will push the pintle all the way out and it will go flying. So have your assistant start the car, and see if your IAC is working correctly. Last thing before you shut down the engine, slow down the idle so the ECM makes the IAC pintle retract like it was swimming in cold water. This will allow you to re-install your IAC without the pintle bottoming out before its fully inserted.

The IAC is a stepper motor, so you can't just apply 12 volts to the windings and expect it to do anything. You can do resistance checks on the windings as described already, but that's about all you can do besides connect it to the ECM and go through the IAC reset procedure. I know there are IAC diagnostic procedures outlined in the GM/Helm Factory Service Manual, but I haven't looked at them recently.

[This message has been edited by Marvin McInnis (edited 07-20-2010).]

Sun drop is correct !! but for the average Fiero owner pull the IAC ,,connect the wiring and have some one turn the key on,,the pintle should move in or out ..
if an IAC passes this diagnostic test ,,95% its OK..

quote Originally posted by uhlanstan: IAC code Procedure for the novice ,, check things listed for code 35 if this does not work ..pull snorkle, spray carb/injector cleaner in TBI wipe it clean,,now eyeball IAC hole you will see it by theTBI throttle plate .spray directly in hole for 5 seconds,wait a minute and blast it again for 5 seconds.. This is how they do it in the big time certified fancy smancy gar-rage with clean floors clean tbi throttle area,, wipe with lint free rag,,now with engine running at 1100 to 1500 RPM,,spray the IAC hole for 5 seconds ..Shut engine down wait 3 to 4 minutes cranker up run engine at 1100 to 1500 RPM and spray IAC hole for 5 seconds,, use spray tube.. some recomend 10 second blast,,5 seconds should do it.. Use Standard or Delco IAC,,many others do not last

Humm sounds strange. Is that some sort of cleaning procedure?

Perhaps I should add, the TB was rebuilt with the recent engine swap and is clean as a bone. I'm thinking now what might have happened was because I pulled an IAC of another TB and put in to, I might have jammed the pintle in to the TB and messed up the servo.

[This message has been edited by Seanpaul (edited 07-21-2010).]

quote Originally posted by Seanpaul: What terminals do you apply voltage to make the IAC retract???? This would be nice to know for future when installing used IAC's form other engines. I think the pintle might have been extended to far when it was installed...

That was my point ... you can't just "apply voltage" to a stepper motor. A stepper motor requires short pulses applied to two or more different windings in a particular sequence. You pulse them in one order for the motor to advance in one direction, and in a different order to run the motor in the other direction. Each set of pulses moves the motor a precise, predefined step increment.

I agree that if the pintle is extended when the IAC is installed into the throttle body it can jam, and according to the FSM that can permanently damage the IAC motor assembly.

If the IAC pintle shaft has slots on the side, you can press on the pintle while rocking it side to side and make it retract. If it has a round shaft, you can push the spring away from the pintle head and rotate the pintle to make it retract. If the spring tangs don't align into the slots in the back of the pintle head, rotate the pintle further until the spring snaps in. The adjustment length is 1 and 1/8 inches or slightly less, from the gasket seating shoulder of the IAC body to the tip of the pintle. This is with the gasket removed from the pintle. If the install length is greater than 1 1/8 inch, you stand a chance of damaging the IAC when you install it.

There are two styles of IAC's. One has the terminals recessed into the end, and the other doesn't. Every one I've ever seen on a Fiero has been recessed and uses a weatherpak connector.

Code 35... Likely has a Vac leak.
See 86SM or 88SM, Code 35

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Dr. Ian Malcolm: Yeah, but your scientists were so preoccupied with whether or not they could, they didn't stop to think if they should.
(Jurassic Park)

The Ogre's Fiero Cave (It's also at the top and bottom of every forum page...)

quote Originally posted by Marvin McInnis: That was my point ... you can't just "apply voltage" to a stepper motor. A stepper motor requires short pulses applied to two or more different windings in a particular sequence. You pulse them in one order for the motor to advance in one direction, and in a different order to run the motor in the other direction. Each set of pulses moves the motor a precise, predefined step increment. I agree that if the pintle is extended when the IAC is installed into the throttle body it can jam, and according to the FSM that can permanently damage the IAC motor assembly.

Ohh. I thought I remember years ago the smog tech at the shop i worked at retracting a IAC with a 9volt battery.

9v Battery - Not a Fiero IAC.

You can however

Extend the pintle - jumper A-B on the ALDL and turn the key to the ON position. This will cause the IAC to run the pintle all the way OUT of the IAC body. Installed the pintle will stop when it gets seated in the throttle body. Do it with the IAC out of the throttle body and the pintle might come all the way out and go flying. Remember the pintle needs to be retracted when you install the IAC.

Retract the pintle - no A-B jumper. This works if you have a second IAC and your idle slows down to the correct speed. If you have a vacuum leak and the idle won't slow down enough this won't work. Have one IAC installed in the car. Take off the intake snorkle. Start the car with the installed IAC plugged in. The car should start and the idle should settle down to the correct speed. Looking into the throttle body note the round hole. This hole feeds the IAC passage. Put your finger on the hole fully covering it. - This SHOULD kill the engine. If it doesn't kill the engine either you have a vacuum leak or a perhaps a mis-adjusted throttle. If your troubleshooting a code 35 and this doesn't slow the engine speed to below idle - then your problem is NOT with your IAC. Your IAC would be fully closed and the engine would be idling to fast. And that's what code 35 means - The ECM can't properly control the idle.

So now I am assuming covering the hole drops the idle to below what it should be. Unplug the installed IAC and plug in your second IAC. Now cover the hole with your finger to the point that the engine is running below proper idle. The ECM will make the IAC retract it's pintle to increase the idle.


If your so interested to watch the IAC work both ways - you could unscrew the installed IAC a bit (pre loossen it) which would make the engine run above idle (finger all the way off the hole). Again with the ECM should push the pintle out in an attempt to slow the idle. Don't let the pintle come all the way out and go shooting.

You can also use the finger in the IAC hole described in my previous post to test your IAC operation.

yellow thing in there just for illustration


IAC FEED HOLE

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As stated before in this thread - IF your idle is always too high, and you have a code 35 it's most likely NOT an IAC problem but instead a vacuum leak problem

[This message has been edited by phonedawgz (edited 07-21-2010).]

" Put your finger on the hole fully covering it. - This SHOULD kill the engine."
"So now I am assuming covering the hole drops the idle to below what it should be."

hummm...confused on what should happen when covering the hole....

I started the car, and covered to hole right away, it died.
I then started the car waited a few seconds, then covered the hole and it lowered the idle below 1k.

What does this mean?

I did run a propane can with vacuum line around the intake, and egr area. I didn't notice any change in RPM's so I don't think I have a vac leak.
But then again, I also thought I can use a 9 volt battery to retract the IAC valve. lol.

Well since it killed it, that shows you don't have much of a vacuum leak if any.

So when you had the second IAC plugged in and you made your engine run below normal idle the pintle of the second IAC should have retracted. It would show that your ECM can retract your pintle.

So what did the pintle do when you did this. Mine did retract when doing this.

When you cover the idle air hole the car should die. It's the only place the engine should be receiving air at idle. If the car does not die then you either have a vacuum leak or your throttle plate (butterfly) is misadjusted. Is the cover for the throttle plate stop screw missing (aka idle screw)?

BTW, what is your idle RPM?

For resetting the IAC: you are simply trying to set the IAC to a known point for the ECM. Jumper A & B pins on the ALDL plug. Turn key to ON. Walk to the engine compartment and wait 30 seconds. (If it's quiet you can hear the IAC making a clicking noise) The pintle is being driven fully closed (extended). Now disconnect the IAC electrical connector with the ignition key still ON. Once disconnected then turn the key OFF. Now reconnect the IAC motor and remove the jumper from A & B pins.

quote Originally posted by phonedawgz: Well since it killed it, that shows you don't have much of a vacuum leak if any. So when you had the second IAC plugged in and you made your engine run below normal idle the pintle of the second IAC should have retracted. It would show that your ECM can retract your pintle. So what did the pintle do when you did this. Mine did retract when doing this.

Well the problem is I didn't have a good IAC to use to see it if was retracting. Turns out the IAC valves that I had left over, the little white plastic keyway guide that guides the keyway on the shaft is broken. So the whole pintle rotates instead of the guide holding the pintle steady on the keyway base. < Did that make any scene?

I did however hear the mortor trying to move the IAC valve.

The cover for the throttle plate stop screw is literally a blank metal cover over a screw that the factory put into place to keep people from trying to adjust the throttle plate. You know the ECM handles idle through the IAC motor. Some people mistakenly try to adjust idle as if the throttle body was a holley carb. They physically remove the cover over the throttle plate stop screw and try to adjust the idle by opening or closing the throttle plate with the stop screw. In reality the stop screw is simply to keep the throttle plate from closing too far and getting stuck in the throttle body bore. Nothing more.

Now in this picture look at the part labeled "idle screw". This hole is supposed to have a blank cover over the screw. If you can see the screw then it has been tampered with.



And make sure this pipe is stuck into the back of the throttle body and into the lower intake. If it leaks your idle will be high.

[This message has been edited by Hudini (edited 07-22-2010).]

So if covering the IAC hole doesn't kill the engine, and you prob have a fast idle problem. You most likely have a vacuum leak. That will cause the fast idle. That will cause the code to set because the ECM can't get the engine to idle at the correct speed.

Most 2.8 vacuum leaks cracks on the EGR tube. You have to take the insulating blanket off of the tube to see the cracks

quote Originally posted by Hudini: The cover for the throttle plate stop screw is literally a blank metal cover over a screw that the factory put into place to keep people from trying to adjust the throttle plate. You know the ECM handles idle through the IAC motor. Some people mistakenly try to adjust idle as if the throttle body was a holley carb. They physically remove the cover over the throttle plate stop screw and try to adjust the idle by opening or closing the throttle plate with the stop screw. In reality the stop screw is simply to keep the throttle plate from closing too far and getting stuck in the throttle body bore. Nothing more. Now in this picture look at the part labeled "idle screw". This hole is supposed to have a blank cover over the screw. If you can see the screw then it has been tampered with. And make sure this pipe is stuck into the back of the throttle body and into the lower intake. If it leaks your idle will be high.

Ok So check:

(1) Idle Screw
(2) Vacuum Tube
(3) EGR Tube.

I was wondering about that vacuum tube. The o ring in the TB looked old, and the rubber part has no clamps. Should it?
Also my EGR tube has a nice new shiny heat covering. I just assumed it had no cracks. Guess I have to cut that stuff of and inspect it?

See the engine starts out high idle at codl start, then it idles down perfect when warm. But the light comes on (Code 35) during driving,
then after that it stays on and when I slow down the engine surges when I'm trying to creep in 1st gear. Does that help narrow it down any?

Could I run a vacuum hose of propane around these areas and see if the idle goes up?
Does that old trick still work? Thanks a lot for your help guys. It's nice to learn new things!

[This message has been edited by Seanpaul (edited 07-23-2010).]

So it's warmed up - what is the idle?

Stick or auto?

Idle in gear and in park if auto?

Code 35 comes on when your idling while you're driving right?

[This message has been edited by phonedawgz (edited 07-23-2010).]

quote Originally posted by phonedawgz: So it's warmed up - what is the idle? Stick or auto? Idle in gear and in park if auto? Code 35 comes on when your idling while you're driving right?

tits on at 1k.
Stick.
If in first gear car lunges/surges between 1k and 1200. Very slight surge, but very noticeable once inertia picks up.
Code 35 when driving at freeway speeds.

I did notice last night however, that once the light code 35 comes on, then when i putt up to a stop light it surges at idle between 1k to 1400k.

It should only come on when your at idle. I'm thinking maybe your TPS is bad.

quote Code 35 - Idle Speed Error Trouble Code 35 indicates that the closed throttle engine speed is at least 150 RPM more or less than the commanded idle RPM for 20 seconds. The conditions for setting this code are: Idle speed is 150 RPM more or lessthan commanded idle speed The above conditions exist for over 20 seconds. Typical causes for this code include: If the idle speed is too high, look for vacuum leaks or air paths around the IAC If the idle speed is too low, look for restrictions in the air path, too lean or rich mixtures Mixture too lean Mixture too rich Blockage of the IAC with deposits or "coke" A/C Compressor or Relay failure Defective ECM

Why would the code 35 come on while your driving down the highwy unless it things the throttle is closed (tps)

Put a volt meter lead on the blue wire and the other to ground. Turn the key on and check the voltage. It should start at about 0.5 and as you open the throttle it should move up to 4.5 - 5. If it drops out to zero at some point, that is most likely the cause of your trouble.

[This message has been edited by phonedawgz (edited 07-23-2010).]

Yea. It weird you mention the TPS. I felt more like it was a TPS problem all along, as the surging at steady throttle is a common TPS problem. I guess I just assumed the code 35 was specifically for IAC. But I also know how one symptom can cause the computer to confuse it with another. I'll go out and check today.

phonedawgz, is the above ok?

Yep - Your TPS tests good

ok. so I'll check for vac leaks, then is none assume i need a new IAC. lol.

Your speedo works right?

quote Originally posted by phonedawgz: Your speedo works right?

Yes.