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How to Idle Re-Learn after Battery Disconnect!

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639K views 103 replies 71 participants last post by  Cooper67 
#1 ·
Posting here as this seems to affect some Forester and Imprezza models with Electronic Throttle Bodies or IACV that undergo a battery disconnect, and lose their idle calibration.

As per these links to retrain the ECU idle parameters:

My idle relearn procedure:
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1) Turn off the lights, aircon, stereo or any system in the car that draws extra current on top of the engine.
2) Disconnect the battery for 30 mins.
3) Reconnect the battery.
4) Before you start the car for the first time, turn the key to the ON position but do NOT turn the engine over. Wait 10-15 seconds so the electronic throttle body or IACV has time to go to the factory programmed home position.
5) After waiting, start the car and let it idle without any load, lights, A/C etc.
6) Every 20 seconds or so the idle will be adjusted up and down as the ECU tries to adjust it towards a stoichiometric fuel / air mix.
7) Leave the engine running for a full 10 mins but DO NOT TOUCH THE ACCELERATOR during this time or turn on anything that will cause extra electrical current draw.
8) Turn off the engine, and leave the key in the OFF position for at least 20 sec.
9) As per step (4) turn the key back to the ON position for 10-15 sec without actually starting the engine.
10) Start the engine and leave to idle for a further 5 minutes without touching the accelerator and without turning on other systems in the car.
11) Turn off the engine again and wait at least 20 sec before restarting.
12) Take the car for a test drive as the ECU should now be fully retrained.
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I know for a fact that this is necessary for the 2003 Forester XT because this process seems to have been the cause of all the teething problems with the LPG system because it was never retrained after the battery was disconnected during the conversion. I used an OBD2 adapter to measure the AFR beforehand - and the LPG AFR was waaay out in comparison to the petrol. After following the process above both sets of AFRs are now very close to a stoichiometric mix, and the car idles correctly without the revs bouncing up and down constantly.
 
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#2 ·
What a load of B.S. Internet mythology. I mean I'm glad it worked for you, but my battery has been disconnected dozens of times with no special "training" afterwards. I have a hard time believing any competently designed car would require a spurious mystic undocumented ritual to reset it after a battery disconnection!

-- Steve
 
#3 · (Edited by Moderator)
1) Calling BS just because you haven't needed to do this yourself isn't very helpful and is a good way to put people off posting up hints and tips in future.

2) Its common knowledge that certain ECU parameters are lost when the ECU is reset (fuel trim corrections etc.) so its not all that unreasonable that the idle position is also lost given that the ECU doesn't necessarily know in advance whether its running on 95 RON, 97 RON or 99 RON in order to adjust the fueling.

3) One of the linked posts is to this very forum (albeit a different area) - with several other SubaruForester.org posts outlining the same process of retraining the ECU as the solution of idling problems - and people commenting that it worked for them. Some people even quoted that the process is outlined in their manual - but its not in my UK spec manual.

4) I was initially skeptical but decided to give it a try because THIS POST refers to the ECU having to send a signal to the injectors to 'catch' a rapidly falling rpm level (e.g. dipping the clutch) and if the ECU doesn't send this signal in time then the engine can drop to low rpm and be on the verge of stalling for a few seconds. These were the exact symptoms I was having on both petrol and LPG.

5) Petrol seems less susceptible to the problem than LPG - but that doesn't mean the problem isn't occurring on petrol. As per comment #4 dipping the clutch and watching the point at which the needle stops falling is a good way to see whether you have a problem. If the needle dips to 500rpm or lower then the ECU isn't sending the injector pulses quickly enough to hold the revs at the normal idle level.

6) If you miss the symptoms in the first week or so after a battery disconnect then the idle correction still keeps learning - as does the long term trim correction. As a result the car will usually sort out the idle problems after a week of running.

7) Before I trained the idle the AFRs were off - with both petrol and LPG not getting to a stoichiometric mix very quickly after letting the revs drop to idle. After training then on both fuels the AFR drops immediately to 14.5:1 to 14.8:1 which is almost bang on an ideal stoich mix.

8) During the process you can actually see the ECU raising and lowering the idle slightly every few seconds as it hunts for the optimum level. On subsequent engine restarts the engine dropped immediately to the same idle level as the end of the training - lending credence to the fact the ECU is actively learning the idle position.

Given that this process takes very little time and effort then I think its worth trying if you have already ruled out MAF, O2 sensor and vacuum leaks as the likely causes of any idle problems.
 
#4 ·
Sorry but I'm in the BS camp here too. Well, not BS but way overcomplicated. I've used the Vishnu method dozens of times.

Turn off everything. Disconnect the earth strap. Hit the brake pedal to use any residual current. Wait between 5 seconds and 2 days. Reconnect the battery. Drive without using boost to a road that is preferably long and straight and slightly uphill. Start to accelerate allowing boost to rise slowly and without getting too much. Continue for 30 seconds or thereabouts. The end. Your car will now idle and accelerate more smoothly and feel a little more powerful. If you haven't done this for a long time or even ever the effect will be more remarkable.
 
#95 ·
Sorry but I'm in the BS camp here too. Well, not BS but way overcomplicated. I've used the Vishnu method dozens of times.

Turn off everything. Disconnect the earth strap. Hit the brake pedal to use any residual current. Wait between 5 seconds and 2 days. Reconnect the battery. Drive without using boost to a road that is preferably long and straight and slightly uphill. Start to accelerate allowing boost to rise slowly and without getting too much. Continue for 30 seconds or thereabouts. The end. Your car will now idle and accelerate more smoothly and feel a little more powerful. If you haven't done this for a long time or even ever the effect will be more remarkable.
I realize this is very old and I’m only posting for anyone else who may stumble across this. But how is what you are recommending ANY different from what the op suggested with the exception of semantics? “Run out the electric, perform some kind of base idle learning etc” that’s crazy to say his is bs but
Yours is not?
 
#5 ·
Sorry about the tone of my earlier reply. Like I said, glad it worked for you, but I am pretty sure that the ECU will perform what little learning it does during normal driving. Maybe LPG changes that for some reason.

-- Steve
 
#9 · (Edited)
You don't need to do this; also there is no need to disconnect the battery for 30 mins. My AM (so I guess all similar eraseable data) go back to default as soon as the battery is disconnected.

If the OP encountered a problem that was due to the fact that the petrol ECU didn't have a chance to recalibrate hence the LPG ECU was calibrated using the wrong baseline.

If you don't use LPG it will take as long as it takes for the petrol ECU to recalibrate, there is no big deal (similarly with the AM going back to 1)
 
#10 ·
You don't need to do this.

If the OP encountered a problem that was due to the fact that the petrol ECU didn't have a chance to recalibrate hence the LPG ECU was calibrated using the wrong baseline.

If you don't use LPG it will take as long as it takes for the petrol ECU to recalibrate, there is no big deal (similarly with the AM going back to 1)
So it may well help Tumble then?
 
#13 · (Edited by Moderator)
Technically you do :icon_razz:

I found earlier today that running an ECU Fault Code reset using the Torque Pro application via OBD2 adapter actually triggers a FULL ECU reset, which clears out the codes but also the trim correction data, and yes - you've guessed it, the learned idle position too.

If I drove the car on ONLY petrol immediately after the reset (with no learned idle) then the original problem of low idle (bordering on stalling) returned immediately, and didnt get any better after 15-20 mins driving.

I then did another reset and this time did the ECU learning on petrol alone. After only 5-6 mins of stationary idling with everything turned off except the engine it had settled down to a steady idle. I then took it for a quick spin and it was running perfectly fine without fault.

I then reset again - and the idle fault returned immediately.

Finally I did another reset and did another idle learning session - this time swapping between petrol and LPG during the session. It took slightly longer before the idle was fully settled - but once it had the AFRs and Fuel Trim Corrections (both short and long term) were settling extremely quickly. In fact swapping between LPG and petrol the ECU was managing to move the long term trim correction average within 90 seconds of changeover, which is pretty damned good in my opinion. All idle AFRs were also VERY close to a stoich mix on both petrol and LPG.

:woohoo:

So as far as I'm concerned its worth performing on any car showing a rough idle. I'm still investigating the cause of my idle problem, and will check the vacuum hoses and throttle body at the weekend to see if there is an underlying problem that's throwing the default idle position off slightly.

HOWEVER - as the car was originally LPG mapped with the idle fault in place, and the AFRs all over the place then I will have to go back for a remap tweak - especially as I'm still getting occasional P0171 codes indicating its running slightly lean with low throttle (perversely its fine on WOT!). I have also configured Torque to show the Fuel Trim corrections so I will be monitoring them when the CEL next appears to see if its the short term or long term figure that's raising the fault code.
 
#12 ·
good stuff :)

should i do the whole process on petrol, on gas or both?

im guessing petrol to create the correct baseline.

about the time my stalling happened was when my old battery was failing, so i presume every time it was dead i would end up with the wrong idle point.

once sorted id of thought i could get away with taking off the low end lean - which i think is causing the odd engine surge i mentioned in bods other post when warming down on gas. (checked today and it dosn't happen on petrol)
 
#14 ·
Replaced my car battery 1 week ago and my fuel consumption is over the chart (21litres per 100km) usually would be around 10-12 litres. So i saw this thread and wondered if I should do it. So I call my SUbaru dealer and he told me that I had to do the idle relearn with my 2010 Subaru Forester. So I will give this a try for sure.

Thanks BOD.
 
#18 ·
Just adding my $0.02 to the conversation of CEL: P0171.

My 2009 popped a P0171 a couple times over the last couple weeks - and the car would rough idle and almost die when coming to a stop at a red light.

I did not have any CRC MAF cleaner, so I tried the Idle Re-Learn steps with no luck.

Upon getting some CRC MAF cleaner, I removed my MAF and found a piece of dandelion fuzz stuck to the MAF 'sensor wire thingies'. I removed the fuzz & spray cleaned the MAF.

The forester runs great now, no CEL, no rough idle.

Thanks
G
 
#19 ·
Thanks for the reference link to my post BOD. For those claiming BS... say what you want, you're wrong. The process I posted solved the stalling problem I was having in my MT 2005 Forester after I had run the battery dead. I ran the battery dead because I had broken the alt belt and was trying to get the Forester back to civilization. For about a week it stalled whenever it idled, including when I was downshifting on an exit ramp going 50 mph. After I did the "relearn" process the problem went away. I did nothing else, so this process DID fix it.
 
#22 ·
My 02 is running like crap, 1500 rmp it shakes and idles rough. Even wile driving if rmp lower then 2k it runs like crap and even feels like missing/knock. Going to try this before dumping money into her. The TPS was loose so I tightened it to where in think It should be, wires look brand new haven't checked plugs yet(cant find my extension)
Other then that aspect it runs great accelerates great I pulled what I thought was o2 plug see if that would help but was same and didn't even throw CHK engine light so either was incorrect of previous owner pulled CHK Eng Bulb.

Can anyone give picture exact connector of the front o2? Think I have 2.5 supposedly previous owner replaced engine and tranny ...
 

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#23 ·
so I tried to perform this process to solve stalling problems in my 2003 Forester MT, but after reconnecting the battery, waiting the 10-20 sec on ON then starting the engine, it runs for not more than 15 mins then stalls. when I try to start it again it doesn't start for a while till I give it like 30 min to 1 hr. Is that normal? Should idling problem affect subsequent startin?
 
#25 ·
Curious... did you have idle issues after the battery was replaced, or did you follow this procedure as a precaution?

I'm asking because I've never had idle issues on either of our Forester after the battery has been disconnected or replaced.

Bobby...

['07 FSXT Member Journal] ['03 X Member Journal]
 
#26 ·
Just wanted to post that the procedure in post #1 fixed my idle issue AND my rev hang issue. Very happy indeed! I was skeptical at first, but upon multiple test drives the car finally drives normal after the procedure. Also I did not wait 30 minutes after I disconnected the battery, I simply disconnected it, drained any residual charge and immediately reconnected the battery. For the record I have a 2009 Forester 2.5L 5-speed manual transmission.

Thanks!
 
#27 ·
I will have to say that there is some truth to this. Some steps may not be needed, or necessarily required, but when I had to reset my ECU every other day due to a fuel tank sensor throwing a check engine light, there would be sometimes where I would reset it and it would idle horribly all day. I would pull up to a stop light and it would stall out, idle rough, or just be a pain to drive around the city all day.

If I reset the ECU, and perform similar steps as described in the OP's original post, the car would behave correctly and drivability was perfect. I could definitely feel the difference in the car if I let it "re-learn to idle" before just driving it after an ECU reset or battery disconnection.

Even now with the car mended, and NO CEL's at all, I've had the battery out a few times and if I don't allow the car to re-learn to idle, I can feel the difference in the car. I doubt anyone who doesn't REALLY pay attention to their car would notice, but I do. I follow a procedure similar to the OP, and voila. No more issues, sluggishness, stalling or rough idle. So before people start jumping on the BS bandwagon, I suggest possibly realizing that this has worked for some people, and this is not the first time this type of procedure has been recommended for idling/drivability issues.
 
#28 ·
Idle problem solved

I had a new battery installed and immediately started experiencing idle problems. I went back to the vendor and they did not have a clue. I found this link in the forum, followed it explicitly, and now my car idle problem was fixed. I am not here to say that there might have been a short cut, but I don't care my car is happy and so am I. Thank you for your help. Richard

P.S. I have an 06 Outback with 110,000 miles on it. Still running like new and getting 33 MPG on highway.
 
#30 · (Edited)
IDLE /STALLING REMEDY:

Thought I Would post a simpler solution to a stalling problem with my forester.

I did this last year after putting in a new battery and I just phoned and double checked with my Subaru mechanic in Oakville. I had clutch replaced yesterday and they didn't reset the idle so after the mechanics (not a Subaru mechanic) they didn't realize they needed to do a resequencing.
Instructions:

Do this when the engine is already warm

Idle the vehicle until the engine fan comes ON (takes about 20 min on a cold engine, sooner if you were already driving it)

Turn on the A/C for 1 min! (crutial to do or it won't reset just idling it).
Turn off the a/C

Continue idle for one min then shut engine off

This relearns and resets the electrical
It should work now

Without doing the reset, it will continue to almost stall or stall as you come to a stop

If it doesn't work for you please call or take it into a Subaru dealer. (calling them for instructions is easier. :).

Good luck. Safe Subaru driving!

P.s- has anyone driven the Hybrid and is it worth getting to save on gas? Thx
 
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