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Old 07-21-2003, 01:09 PM   #1
Yotsuya
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Default Idle Air Controller

I ran a search but couldn't find the info I was looking for. Can anyone help me deduce this problem?

My car had a rough idle; cylinders misfiring, engine shaking, the works. It also affected the car when in gear at low RPMs; it would hesitate, not responding to the accelerator until it was past halfway then surging to the power it should be providing at that level of throttle. It would not do this when revving out of gear.

Anyway, I was directed to several areas. Spark plugs and wires are both less than a year and ten thousand miles old. I checked them and everything was tight. I have also been told the forward Oxygen sensor may be at fault, but further investigation has led me away from that.

I was also directed to the Idle air controller. I pulled it off and cleaned it with a rag (it was black and filthy), and also cleaned out the hole into which the sensor goes. It had no effect for about half an hour of driving, but after a while there was no hesitation when starting in gear, and the engine idled better, though not as smooth as it used to.

This weekend the problem returned. Same rough misfiring idle, same hesitation starting in gear. To test the success of cleaning the controller, I cleaned it again (it had almost nothing on it), and the same thing happened, a half hour later it was almost back to normal.

What I want to know is, is this a sign the idle air controller is the culpret, or is there something else that I'm affecting when I clean it? I'm trying to get hold of an idle air controller to test locally, but I also wanted to see if anyone may have a diagnosis I haven't considered.

Thanks
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Old 07-21-2003, 03:32 PM   #2
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I think your heading in the wrong direction. The IDLE air controller only limits the amount of air entering the engine to control idle speed. Bouncing idle is usually the sign of the IAC acting up.

Oxygen sensors are a wear item, contrary to what many may think. Normal life is 40-60k. Even if they are functioning correctly they start to get slow.

I suggest grabbing a bottle of techron and putting it in at your next fuel stop. Fill the tank 1/2 way, then give your car a good "italian tune up"


Is this most noticable when the car is restarted hot (after driving around and parking for example)?
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Old 07-21-2003, 07:27 PM   #3
Yotsuya
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Quote:
Originally posted by ciper
Is this most noticable when the car is restarted hot (after driving around and parking for example)?
It only comes up after the engine is at temperature; the idle is higher until then.

Sounds like you think the prob;lem ay be in the fuel system; clogged line/injector maybe dying fuel pump. I would be swayed to that if tinkering with the controller didn't noticibly improve the problem.

That said, an injection cleaning shouldn't hurt...
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Old 07-21-2003, 10:43 PM   #4
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I know exactly what your talking about! I’ve been having the same problem and have heard every thing you have said and more. Could be water in gas, TPS sensor, and a couple of other things. The problem for me arose when the car was driven hard, in the upper rpm's for a period of time.....autocross, mountain road ect.... Once the car was driven normally so to speak it wouldn’t be as noticeable but still there. Recently i installed some Borla headers on the car and when i reset the ECU the problem went away for the time being. I also notice that the air condition has an effect on the problem also.

P.S. the problem arose at about 36k

Last edited by Burnout; 07-22-2003 at 12:40 AM.
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Old 07-22-2003, 12:50 PM   #5
Yotsuya
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My problem's at idle and low RPMs in gear. At high RPMs everything's good.
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Old 07-23-2003, 01:36 AM   #6
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The problem happens after i had driven in the upper rpm range, it doesn’t happen in the upper rpm range. My idle will fluctuate up and down and gets worse with the AC on.
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Old 07-23-2003, 05:23 PM   #7
pjcoregon
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here is the decision tree for diagnosing a problem with your IAC.


http://www.geocities.com/kuleshoff/IAC.htm

Idle Air Control (IAC) Valve
OPERATION

* See Figure 28


The IAC valve increases engine speed when engine temperature is low by venting air into the air duct behind the throttle plate.
On the Loyale, the IAC valve is located on top of the engine, in front of intake air duct. On the Justy, it is in-line between the air filter housing and the intake manifold. On the Impreza, Legacy and SVX, the IAC valve is incorporated into the throttle body.

TESTING

Electrical type


1. Disconnect the electrical harness to the IAC valve while the engine is idling. Check to see that the rpm drops.


if the image does not display... it is here => htp://www.geocities.com/kuleshoff/fig28.jpg


2. Connect the IAC valve connector and check to see that engine rpm resumes its original speed.

!!!Disconnecting the harness causes a change in engine rpm when the engine is cold. However, when the engine is warm, it causes a smaller change, or almost no change at all.


3. Stop the engine, then disconnect the electrical harness from the IAC valve.
4. Turn the ignition switch to the ON position.
5. Using a voltmeter, measure the voltage across power terminal BW on the SAC valve connector and ground. Voltmeter should read 10 volts. If the voltage obtained is less than specified check the harness.
6. Turn the ignition switch to the OFF position. Using an ohmmeter measure the resistance between each terminal of the connector on the IAC valve. The ohmmeter should read 7.3-13 ohms at -4°F..-176°F (-20°C..-80°C). If specifications are not as specified, replace the IAC valve.
7. Using an ohmmeter, measure the insulation resistance between each terminal of the connector on the IAC valve and ground. The ohmmeter should read 1 mega-ohm. If specifications are not as specified, replace the IAC valve.
8. Connect the IAC valve harness, then disconnect the control unit electrical harness.
9. Turn the ignition switch to the ON position. Using a voltmeter measure the voltage between terminal 45 (GR) of the control unit harness and ground. Voltmeter should read 10 volts. If specifications are not as specified, check the harness between the IAC Valve and the control unit.
10. Turn the ignition switch to the OFF position, then connect the controls unit harness.
11. Monitor the voltage across terminal 45 (GR) on the control unit harness and ground, when the ignition switch is turned to the ON position. Voltmeter should read 1 volt for approximately 1 minute after the ignition switch is turned ON and 10 volts after 1 minute. If specifications are not as specitied, check for poor contact of the terminal or a faulty control unit.
12. Turn the ignition switch to the OFF position, then disconnect the IAC valve hose.
13. Turn the ignition switch to the ON position. Look through the open end of the pipe (from which the air control pipe was disconnected) and check that the valve moves from the fully closed position to the fully opened position, 1 minute after the ignition switch is turned to the ON position.

REMOVAL & INSTALLATION


1. Disconnect the negative battery cable.
2. Disconnect the injector [ead wire from the clamp.
3. Remove the IAC valve, gasket and lead wire from the Venturi chamber.

TO INSTALL


4. Using a new gasket, install the IAC valve.
5. Connect the injector lead wire.
6. Connect the negative battery cable.
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Old 08-06-2003, 01:09 AM   #8
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I'm having this same problem as Yotsuya.

His description matches mine exactly. At idle, it hovers around 700 rpm, but is not smooth at all. Whenever at low RPMs, there is definite heitation, in almost any gear, up until 1800 RPMs, from there and up, it seems normal.

So for instance, when doing a rolling stop at a stop sign, put it in 2nd gear, and there is definite hesitation until the revs come up.

Has anyone found a solution to this?

(Just tonight, I took out the 2nd filter, started it back up again, and engine died. Put the 2nd air filter back - the one right before the throttle body - and the hesitation was worse.... the revs would drop so low, that the engine would sometimes die. i drove around, and it seemed to get better. the low RPM hesitation was gone, and when I would stop at a stop light, the RPMs remained steady at around 700)
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Old 08-06-2003, 01:27 PM   #9
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I had the same problem with my 97 L a few months ago. The IAC was definitely the cause of mine- I yanked it out and blasted the inside with carb cleaner. Just buy a big can at your favorite auto parts store for like $3 and really soak the inside of that thing. I also took out some Q-tips and wiped the gunk off the inside as best I could. That was about six months ago and my car's been idling perfect ever since. (this was after I replaced a bad MAF sensor)
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Old 08-06-2003, 07:27 PM   #10
Albert
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A bit OT...but do any of you guys with IAC valve problems use any type of fuel system cleaners on a "regular" basis?
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Old 09-19-2003, 05:20 AM   #11
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Is this why on my 95 Impreza 1.8 when I first start it in the morning when it's cold the Rpms will go 1,000 then under 1,000 then back over 1,000 you can hear it as well.. their is no heitation.. But I did have a rough idle waiting at the light.. I thought the car was close to stalling.. it was 2 lines up from 0 Rpms which I think is 800?
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Old 03-06-2004, 10:37 AM   #12
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I'm also having excactly the same symtoms Yutsuya, has there been any solutions to this problem?

I took off my IAC and it is spotless and operates smoothly, should I clean it anyway?

I also don't have an OHM meter, is there anyway else I can see if my IAC is working properly? (like if I start the car with it off and plugged in should it move?)

thanx
-jeff
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Old 03-07-2004, 01:55 AM   #13
Mapplex
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yes definitely clean it. much of what causes a sticky iac is on the inside and can't be seen. slide that "door" open and blast the inside of that from every angle with carb cleaner.
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Old 03-07-2004, 11:05 AM   #14
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subyluvr2212 cleaned his with carb cleaner and it seriously messed it up, we use brake cleaner to clean ours up.
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Old 03-07-2004, 11:43 AM   #15
Machine Age Victim
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well I dipped my IAC in carb/parts cleaner and it did no good, and it still operates smoothly, is there anyway to open it?

what else could it be causing this problem, does an O2 sensor do this? or PCV?
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Old 06-27-2004, 08:56 PM   #16
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hey guys, try using throttle body cleaner.

I have been having similar problems,
I have a 2000 2.5rs, 57k miles, plug wires have less than 15k on them new fuel filter as well, I cleaned the throttle body and IAC and still same problem, rough idle, worse when AC is on.

-Eric
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