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1999 L
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Discussion Starter · #1 · (Edited)
My Forester L 1999 doesn't pass the inspection because of irregular idle. Here are the symptoms:
Right after starting the engine RPM goes up to about 2000 and then slowly goes down and in a while (in several minutes) becomes less than 1000 and then RPM starts to go from about 500 to 800(sometimes to 1200) back and forth. I know that there are too many possible causes. However what are the most probable causes ? Is there some solution that could fix the problem temporarily ?
 

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2000 2 Outbacks 1Man , 1 Auto
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First place I would check would be the idle speed control motor/valve. Dismantle and give a good spray/clean with carburettor cleaner.
 

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2001 SOLD!
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What is the mileage? The front (Air/fuel ratio) O2 sensor gives that symptom and they NEED to be changed every 100 000 miles. Mine is doing that right now and I have a ScanGageII and the readings for the O2 are freaking out!!!

It will NOT always give you a CEL. I do suggest getting an NGK one. Stay away from BOSCH and Denso!!!!

Hope this helps!!!

:Banane35:
 

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2001 SOLD!
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First place I would check would be the idle speed control motor/valve. Dismantle and give a good spray/clean with carburettor cleaner.
That would also help with the higher idle problem too. Clean it also!!!
 

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1999 L
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Discussion Starter · #5 ·
Thanks all for the answers.
I guess that I can clean idle speed control valve but what about motor ? How can I find out if it doesn not work properly ? Should motor be replaced in that case ?
The milage is about 145000. Upstream O2 sensor was just replaced for Bosch. Is Bosch bad ? Before O2 was changed the RPM went between 500 and about 2000 right after starting the engine.
What is CEL ?
 

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2001 SOLD!
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Thanks all for the answers.
I guess that I can clean idle speed control valve but what about motor ? How can I find out if it doesn not work properly ? Should motor be replaced in that case ?
The milage is about 145000. Upstream O2 sensor was just replaced for Bosch. Is Bosch bad ? Before O2 was changed the RPM went between 500 and about 2000 right after starting the engine.
What is CEL ?
Bosch is Ok, but seem to not last long. Clean your Idle speed control valve. A "CEL" is a Check Engine Light.
 

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1999 L
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Discussion Starter · #7 ·
Thanks for the explanations.

Which way of cleaning of idle speed control valve is safer for the car:
1) mechanical cleaning/spraing of idle speed control valve or
2) http //endwrench.com/images/pdfs/ISCSpring04.pdf ?
The following is for the second option: I didn't find that "GM Top Engine Cleaner (Part #12345089)". Can I use "Carburetor choke & trottle body cleaner" instead ? Some people concern that gaskets/seals may be affected/ruined by the strong cleaner like "Carburetor ...". Is there other safer cleaner that could be used instead ?
 

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1999 L
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Discussion Starter · #8 ·
I have unscrewed and cleaned the valve but that did not help much.
More symptoms. Right after stopping the car (the engine is still running) the RPM is 1000 and stays steady for maybe 15 seconds or so but then I hear the sound like engine is going to stop, and starting from that moment RPM goes between 600 and 900.
Any ideas ?
 

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2001 SOLD!
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I have unscrewed and cleaned the valve but that did not help much.
More symptoms. Right after stopping the car (the engine is still running) the RPM is 1000 and stays steady for maybe 15 seconds or so but then I hear the sound like engine is going to stop, and starting from that moment RPM goes between 600 and 900.
Any ideas ?
Like I said. O2 Sensor. It will not always give you a CEL. I had the same symptoms with irratic idling. It consumed a lot of fuel (Fail safe mode) and ran really weird. I am sure the reason why you aren't passing the test is because of this. Too much unburned fuel being shot out through the exhaust.
 

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1999 L
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Discussion Starter · #10 ·
Which O2 sensor: upstream or downstream ?
I have replaced upstream O2 sensor several days ago. I'm not sure when downstream O2 was replaced. Not recently, but not more than 40000 miles ago. Maybe I should try to clean/replace downstream O2 sensor ?
 

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2001 SOLD!
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Which O2 sensor: upstream or downstream ?
I have replaced upstream O2 sensor several days ago. I'm not sure when downstream O2 was replaced. Not recently, but not more than 40000 miles ago. Maybe I should try to clean/replace downstream O2 sensor ?
Downstream (rear) O2 sensor acts as a sniffer and doesn't control a/f ratio. It just checks to see if the cat cons are working!!!

If it gets problematic, it will usually give a P0420.
 

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1999 L
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Discussion Starter · #12 ·
There was P0420. After replacing upstream O2 the engine codes and CEL were reset explicitly. Can catalitic converter cause the irregular idle ? I don't know when engine codes return after resetting. Is it possible to check for the codes after they were reset ?
 

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1999 L
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Discussion Starter · #13 ·
I have clean the IAC valve but that didn't help.
Did anyone ever succeeded in cleaning of IAC motor ? What did you use to clean the motor ? What about spraying carburetor cleaner into the motor ?
 

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1999 L
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Discussion Starter · #14 ·
It turned out that idle stop screw fell off the throtle body. The edges of the throttle plate became rounder and scratchy. I replaced throttle plate with another one. How to adjust the idle stop screw to the proper position ? How many counter clockwise turns should I make once I start to feel that there is some ( or full ? ) pressure onto idle stop screw ? Right now I have throtle body unmounted. Do I really need to put a new gasket ? The old one looks ok.
 

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1999 L
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Discussion Starter · #15 ·
Solved !

Finally the problem is solved and my forester has passed the inspection !
The last thing that caused irregular idle was MAF sensor ! A mechanic and I tried to clean it but it didn't help much. I managed to break the sensor complitelly, so the engine stalled right after start. However it worker when MAF was disconnected. I was going to buy a replacement at a junk yard but before that I luckily registered my car at subaru.com and immediately noticed a manufacturer's recall of MAF sensor :icon_surprised: The nearest subaru dealer replaced that sensor + added something to the coolant to stop leaks (another recall) for free.
Conslusions:
1) Almost anything in air intake can lead to irregular idle :icon_sad:
2) Register your car at subaru.com and check you recalls :icon_wink:

One more thought: Some time ago the car had engine code P0325 (knock sensors problem) and all the mechanics concluded that the sensor is bad and has to be replaced. It was replaced. However in a while I noticed the absence of the idle stop screw on the throttle body and replaced it with another one. But when I tried to put the new screw in place that little thing bounced out. I found it right on the top of the knock sensor. His predecessor was nearby :icon_cry: Most likely the knock sensor was ok but the fallen screw accidently connected sensor's output with the engine and that caused P0325.
Conclusion N 3) Before replacing something take a closer look at it.
 

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2000 forester s
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Glad to hear you got yours fixed for free. Mine just started doing the same thing pretty much. Unfortunately, when I went to the subaru website, there were no open recalls for mine. :icon_confused: What exactly did they replace on yours, as it is likely to be the same thing on mine.
 

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1999 L
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Discussion Starter · #17 ·
Dealer replaced MAF (mass air flow) sensor. It looks like this one: http://www.scoobyworld.co.uk/catalog/images/mafsensorgif.gif
The MAF sensor is located next to the air filter (very first air filter). Before replacing something you can try to clean everything in air intake: MAF sensor, idle air control valve, throttle body and plate + upper body of the engine + replace air filter(s) if necessary + check hoses. By the way when I had bad upstream O2 sensor the idle became irregular right after start, but when I replaced O2 sensor the idle only became irregular when the engine is warm.
 

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2000 forester s
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I have a upstream O2 sensor in hand and am going to replace it tomorrow. The one on the car seems to have been there since it was recalled in 2001. I doubt its very good either way. If I understand what you said about yours, and we have similar problems, I think that the O2 sensor will be a good fix. I will tell you how it goes, thanks for the info.
 

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1999 L
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Discussion Starter · #19 ·
Don't forget that irreguar idle might be caused by many things. I have read about very different causes with similar symtoms. Good luck !
 

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2000 forester s
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Well I installed the front O2 sensor this morning, and it seems to have fixed the problem.:woohoo: I test drove it for about 5 mins. and let it idle after that for a few more and all sysmtoms seem to have disappeared!! Thanks for the help. I was real glad to see what you had to say about the O2 fixing the running problems, as this was exactly what I had.
 
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