How to relearn idle after battery disconnect.

I posted this in LegUp's Clutch replacement thread, but I thought I'd make a new thread for people who don't know this procedure as per Max Capacity's post.

If that is correct, looks like a great post for a sticky ???

Quoted from a post on the uklegacy.com forums.

Posting here as this seems to affect some Forester and Impreza models with Electronic Throttle Bodies or IACV that undergo a battery disconnect, and lose their idle calibration. Consequently, it may be a solution for some Legacy models.

 

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.

Hope this helps people out. Also, this might be somewhere on the forum already. I just thought it was important enough to have it's own thread.

I don't understand why people make this into such a big deal. The ECU is constantly learning while you're driving, it's not like after a battery reset it just learns for a couple minutes and then stops. Not to mention there's a bunch of other compensations (cold start, hot restart to name a few that relate directly to startup) that also take effect.

The best way to let the ECU learn? Drive the car as your normally would. That's the intent of a continuous closed-loop control system.

After reconnecting the battery, I leave the key in the ON position for about 10 seconds, start the car, and drive away. Has worked dozens of time for me with no issues.

That's basically what I've been doing all these years...

Just drive around like normal, Learning values get reset everytime you flash a map too. Idle will work itself out after 2-3 starts.

-Brian

Those of us with a way to monitor DAM, when ECU is reset it will read as 0.6. I let it idle for a minute, drive around until it's warmed up and then do a few moderate pulls and DAM will read 1.0.

Depends on the tune. Some tuners will have DAM set to 1 after a reset.

After reconnecting the battery, I leave the key in the ON position for about 10 seconds, start the car, and drive away. Has worked dozens of time for me with no issues.

That's basically what I've been doing all these years...

I forgot about that 10 sec period a couple times after resetting codes and was wondering why it took so long to start while cranking.

I wouldn't say there's any one set way to have the ECU relearn. Sure you can accelerate the process of getting IAM/DAM back to 1 by doing a couple pulls so you go through all the load cells but that brings the question of did it really learn anything? I've seen a trick to get IAM up to 1 really quickly of after a reset, do some left foot braking while doing a 3rd gear pull to add load. Never done it as I've always just driven normally and prefer that method personally.

I forgot about that 10 sec period a couple times after resetting codes and was wondering why it took so long to start while cranking.

 

I wouldn't say there's any one set way to have the ECU relearn. Sure you can accelerate the process of getting IAM/DAM back to 1 by doing a couple pulls so you go through all the load cells but that brings the question of did it really learn anything? I've seen a trick to get IAM up to 1 really quickly of after a reset, do some left foot braking while doing a 3rd gear pull to add load. Never done it as I've always just driven normally and prefer that method personally.

That's not a trick, that's just how the ECU learns. Assuming the tune is good (i.e. it doesn't knock), it starts off in coarse-correction mode, and if it doesn't hear knock, it'll increase the DAM until it hits 1.0. Once that happens, it will switch to fine-correction mode. If you put bad gas in the car, and it starts knocking a lot, it'll switch to coarse correction mode and recalculate the DAM until it settles. If it keeps hearing knock, the DAM will drop more, if it doesn't it'll come back up and settle at some intermediate value and return to fine-learning mode. In this way, if you go back to a good tank of gas, and it's learned a large amount in fine-learning mode, it'll re-evaluate the DAM and increase it back up. Generally one or two pulls will stay in a high-enough load/RPM range to cause positive DAM/FLKC changes. If you happen to be at a lower DAM and are trying to re-learn, a couple more pulls will be required to get enough positive FLKC before the ECU changes back into coarse-correction mode.

After I replaced the battery on my car, the idle would hunt and dive (but only) with the A/C switched on. While annoying at first, the idle hunt to 1500 often made the car lurch when stopped in traffic. A few months later, I asked my mechanic to diagnose and fix the issue, but without codes, he was unable to remedy the problem. A bit of searching led to this thread. I laughed at first. Do I have to touch my nose, hold my breath and press the brake release button at the same time? Well, laughing no more. Silly or not, this procedure worked - erratic idle no more. THANK YOU!

Happy Holidays.

If it's a non-turbo, following this procedure has greatly improved my cars drivability after resetting the ecu. I think the car still takes a little time to get back to normal, but it's a vast improvement over the car nearly stalling, and sometimes even stalling when I would shift into neutral or when coming to a stop.

https://forums.nasioc.com/forums/showpost.php?p=34573159&postcount=2

with the engine stone COLD

 

and make sure ALL ELECTRICAL COMPONENTS ARE TURNED OFF.....NO RADIO...NO BLOWER...NO LIGHTS....NO AC NO NOTHING IS ON

 

disconnect the battery.....leave it off for 10 minutes and pump the brake pedal a few times

reconnect the battery...make sure the terminals are CLEAN and tight

 

DO NOT TOUCH THE THROTTLE PEDAL AT ALL

 

get in car

 

DO NOT TOUCH THE THROTTLE PEDAL AT ALL

 

turn the key to the last position before the starter engages and WAIT 10 seconds

 

DO NOT TOUCH THE THROTTLE PEDAL AT ALL

 

turn the key to start the car

 

DO NOT TOUCH THE THROTTLE PEDAL AT ALL

 

leave the car to run until the radiator fans come on.......this may take 20-25 minutes

 

DO NOT TOUCH THE THROTTLE PEDAL AT ALL

 

turn the engine OFF and take the key OUT of the ignition switch and wait at least 10 seconds

 

put the key back in the ignition and start the car and drive normally for a bit and see what happens

When I reset or flash a tune, I simply follow these steps:

- Turn ignition switch to on.

- Turn off all accessories and headlights.

- After 10 sec, start the car without touching gas pedal

- Let idle for 10 min (I use the elapsed time on the clock)

- Shutdown

- Start back up, and drive like normal

If I just reset and drive, it'll die at a stop for several trips; this way is super smooth when it's time to drive.

I see that there's a point in letting the car learn the correction mix for the temperature range when warming up, it will at least take care of those unnecessary engine stops when you stop at a stop sign.

It may take a few driving cycles before it's fully adapted to the situation, just drive the car softly for a few days so it will have time to adapt.

I always let the gauges cycle completely before starting the car anyway, to give the fuel pump time to charge the system and then let it idle for a minute or so and drive it. It will relearn on it's own.

This is pretty much the way I start both cars. I buckle the seat belt while waiting for a gauges to sweep.

Just cycle the key on and off leaving it on long enough for gauges to cycle a few times to prime the fuel pump and let it idle for at least 10 minutes without any throttle input. I know things; my Legacy only burns a qt every 500 miles

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I must admit that disconnecting the battery for a few hours while I was working on the CV boot was NOWHERE NEAR as bad as resetting the ECU with my OBDII reader and software. This disconnect just affects the idle which quickly corrects itself after a few minutes of the engine running in neutral.

I really wouldn't recommend the ECU reset unless you really have to do it, it was a total pig, probably because it reset everything to factory including the long term trim settings. Hard to start, no idle at all, barely managed to keep the engine running while driving it until it sorted itself out.