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2003 Forester
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Discussion Starter #1
This is specifically about a 2003, and it is a friend's Forester, but it should pertain to many other years using the 2.5 engine.

The idle speed in gear (auto trans) has been going lower over the past year or so. It first, it was about 600rpm in Drive, which was not causing a problem aside from "feeling and sounding" awfully low. At that point, I cleaned the throttle body for the owner, and remove swapped the ICV in my '03 with the subject vehicle (after cleaning out the IVC passages that were partly carboned up) knowing that the idle speed is not adjustable, and is commanded by the ECU via the ICV . NOW, the idle in gear is about 500rpm and that can cause hesitation or stumble when accelerating from a stop.

Obviously if there were anything in the intake system causing the low idle, the ECU would command the ICV to open a bit more raising the idle to the rpm value hard-programmed into the ECU, so substituting a known-good ICV from my engine should have allowed the rpm to respond and comply, though both ICVs in my Forester kept a good idle in idle, in Drive, or when the A/C compressor .was engaged, or the aux cooling fan came on.

This makes me think there could be a problem with the ECU or the control wiring to the ICV. I would think that if the OBD II system doesn't "SEE" the ICV, however, the Check Engine would illuminate and a DTC would be recorded, but there's no Check Engine or DTC set.

Any ideas if I am missing something here? Can a dealership computer adjust the idle speed by re-flashing or anything? Throttle position sensor?

THanks,
Bob
 

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2007 Forester Sports XT 4EAT
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2003 Forester
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Discussion Starter #3
The 2003 does not have an electronic throttle body and uses a cable operated butterfly in the 100% mechanical throttle body.

It has a mechanical stop, and if the idle speed needs to be elevated from the nominal speed allowed by the throttle stop, a motor operated plunger controlled by the ECU changes position to allow extra air to bypass the throttle plate (butterfly) increasing the idle speed until it matches the computer programmed rpm.

For instance, if the transmission is shifted from neutral (no load) to drive (load), the Idle Control Valve (plunger) is adjusted to raise the idle speed back to the programmed value. Again, if the A/C Compressor is engaged (more load) the plunger is moved more to admit more air through the bypass passageway allowing the rpm to return to a higher rpm.

In MY case, the ICV apparently is NOT bypassing the additional necessary to raise the idle enough to maintain proper rpm.

But without a DTC, it's hard to know what is going on.

Bob
 

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2007 Forester Sports XT 4EAT
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2001 Forester
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I agree with @bobinyelm , this idle relearn procedure does nothing for the earlier models (SF), models that have mechanical throttle linkage. I have disconnected my battery dozens of time. And then when reconnected, and start the vehicle up, the idle for the first 30 secs is not normal. And then that's it. Never needed or wanted to go through the 10+ steps.
 

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2007 Forester Sports XT 4EAT
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@bman400 I'm just pointing out that there are posts in that linked thread, made by pre drive by wire owners, that say it helped. In addition, the process is more than just disconnecting the battery, it's an ECM idle relearning procedure.

I've never needed to do an Idle relearn, but some member seem to always have this issue? It's surprising how many members have had suscess with the idle relearn procedure.

As I noted, this only costs a bit of your time. If it doesn't work, then you can move on with the troubleshooting.

Bobby...

['07 FSXT Member Journal] ['03 X Member Journal]
 

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2003 Forester
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Discussion Starter #7
I certainly did not mean to ignore a valid procedure and apologize to you personally (especially since you reminded me a couple of times I didn't reference trying it).

Believe me, your feelings are important to me and I would not have intentionally of hurt them, but your post referenced the ETB, which the 2003 does not have. I should have mentioned that the previous time I tried to help my friend I DID the re-learn, even though there was a note regarding the re-learn applying to ETB. I should have realized that you were aware that the 2003 model does not have an ETB and wanted me to try it anyway. Just because it didn't work when I first tried it does not mean it might not work if I were to try it again.

The next time I see Mary Ellen, I will try the re-learn, and will refrain from further troubleshooting as you suggest until I have tried it over. Maybe I missed something last time after-all.

I will report back when I have done so. It may be a few weeks since with Covid she sticks pretty close to home, but I posted here because she took it to an indy Subie specialist, and she texted me that got the car back the same, and I was trying to save her a trip to the dealer (in case their more sophisticated computer can adjust set-speed) if someone had an idea.

Maybe given the car sometimes dies on throttle application now* in gear I should just advise her to make an appt with the dealer given that this could present a dangerous condition in traffic-

Bob

*In the past it idled low but wouldn't die on throttle application




Bob
 

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2007 Forester Sports XT 4EAT
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@bobinyelm it's difficuilt to troubleshoot from afar, no first hand experience with idle issues, so I can only offer what I've seen here on the forum. ;)

The other thing that comes to mind is on this thread. Again, not saying this is causing your issues, but just another thing to consider.

Bobby...

['07 FSXT Member Journal] ['03 X Member Journal]
 

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2003 Forester 2.5X 5MT & 2008 Impreza WRX 5MT & 2009 Impreza 2.5i 5MT
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Who says the idle speed is not adjustable? Do you want to increase the idle speed or do you want to figure out what is causing the low idle?
 

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2001 Forester
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@greengoblin68, unless someone has previously tampered with the idle speed screw, pretty much any new vehicle today unlike the old carb vehicles, there is never any need to be adjusting the idle speed screw. The OP is describing symptoms of something causing the low idle speed.
 

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2003 Forester 2.5X 5MT & 2008 Impreza WRX 5MT & 2009 Impreza 2.5i 5MT
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@bman400 there is no screw to adjust the idle. To adjust the idle you have to use software like FreeSSM or JDMscan
 

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2001 Forester
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That's another reason why one should not be adjusting the idle. Look in the old days, idle needed to be adjusted because you needed to adjust dwell and timing, carb mixtures. All these procedures needed to be done at specific idle speeds. And each adjustment in turn affected the idle speed. With todays Fuel Injection and computer controlled timing, there is no reason to be adjusting idle, unless someone tampered with it in the first place. And the OP has not tampered with the idle previously.
 
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