Fly By Wire - Idle re-learn.
16 February 2018, 12:40 PM
#1
Fly By Wire - Idle re-learn.
I have stolen this from the Bod on the UK Legacy forum. It worked for me, with better MPG, drive-ability and may be of interest to those with fly by wire cars.
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.
Using OBDII adapter + Torque application to do a 'Clear Fault Codes' does indeed trigger a full ECU reset - which can be proven by comparing the value of the long term fuel trim correction before and after the reset.
After each reset you need to allow the car to idle long enough for the short and long term trims to re-settle.
The instructions above are for users without access to live ECU data - and 10 mins will be sufficient for the trim values to stabilise after starting with a COLD engine.
Using live ECU data I can do a reset on my Fozzy, and the trim values will settle within 4-5 minutes if the engine is already warm.
HOWEVER - note that there are actually 5 bands with trim values, based upon engine load and rpm. They **all** get reset at the same time - but only the 'Band A' values affect idling. The other values need you to drive the car on the road - and may take a few hours of total driving time before they have finished settling again.
Regarding LPG versus Petrol for idling to a certain extent it doesnt really matter, because the system will learn and adapt on the road. The big difference is allowing it to train and establish base fuel trim values to start with - otherwise you can get problems with the revs dropping too low at idle etc.
I usually train the Fozzy with LPG - but only because Im still chasing down a huge air/exhaust leak (hopefully to be fixed this Thursday!) that has my fuel corrections running in excess of 15% on petrol, and 10% on LPG.
NOTE: The idle training needs to be without any additional engine load applied. If you train the car with stereo, aircon and heated seats all turned on then the basic idle position will be calibrated for that set of circumstances - which is fine until you start turning them off again!
The idle is temperature dependent - and if you monitor the fuel trims from cold you will see for the first few minutes its enriching the fuel mix over typical warmed up levels.
In fact, if you do the idle re-learn then you can monitor the freshly zeroed long term trim value and it doesnt actually start the learning process until the engine temperature rises sufficiently high - in the case of my Fozzy 74 degrees celsuis - after which time it starts trying to balance short and long term trim values to keep a stoichiometric fuel-air mix.
My old 2.5 Legacy used to do similar with the idle from cold - I suspect that by blipping the throttle you are forcing the engine out from its 'idle' state and putting it temporarily into one of the other states that uses different fuelling information.
The trim corrections have 5 bands, which are referred to by ROMRaider as A, B, C and D (with the 5th being Wide Open Throttle - WOT). The A band correction is only for idling - whereas the B and C bands are for light engine loads and cruising. The D band is usually enriched further as thats used for heavier engine loads and the transition into Open Loop Fuelling (i.e. ignoring lambda sensor feedback and only using the ECU fuel maps at higher RPM).
So - when you start the car its cold and in band A. Blipping the throttle forces it into band B or C temporary - followed by you setting off in the car on your journey. By the time you next come to rest the engine has warmed slightly and the ECU doesnt need to enrich the A and B bands as much - resulting in lower idle.
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.
Using OBDII adapter + Torque application to do a 'Clear Fault Codes' does indeed trigger a full ECU reset - which can be proven by comparing the value of the long term fuel trim correction before and after the reset.
After each reset you need to allow the car to idle long enough for the short and long term trims to re-settle.
The instructions above are for users without access to live ECU data - and 10 mins will be sufficient for the trim values to stabilise after starting with a COLD engine.
Using live ECU data I can do a reset on my Fozzy, and the trim values will settle within 4-5 minutes if the engine is already warm.
HOWEVER - note that there are actually 5 bands with trim values, based upon engine load and rpm. They **all** get reset at the same time - but only the 'Band A' values affect idling. The other values need you to drive the car on the road - and may take a few hours of total driving time before they have finished settling again.
Regarding LPG versus Petrol for idling to a certain extent it doesnt really matter, because the system will learn and adapt on the road. The big difference is allowing it to train and establish base fuel trim values to start with - otherwise you can get problems with the revs dropping too low at idle etc.
I usually train the Fozzy with LPG - but only because Im still chasing down a huge air/exhaust leak (hopefully to be fixed this Thursday!) that has my fuel corrections running in excess of 15% on petrol, and 10% on LPG.
NOTE: The idle training needs to be without any additional engine load applied. If you train the car with stereo, aircon and heated seats all turned on then the basic idle position will be calibrated for that set of circumstances - which is fine until you start turning them off again!
The idle is temperature dependent - and if you monitor the fuel trims from cold you will see for the first few minutes its enriching the fuel mix over typical warmed up levels.
In fact, if you do the idle re-learn then you can monitor the freshly zeroed long term trim value and it doesnt actually start the learning process until the engine temperature rises sufficiently high - in the case of my Fozzy 74 degrees celsuis - after which time it starts trying to balance short and long term trim values to keep a stoichiometric fuel-air mix.
My old 2.5 Legacy used to do similar with the idle from cold - I suspect that by blipping the throttle you are forcing the engine out from its 'idle' state and putting it temporarily into one of the other states that uses different fuelling information.
The trim corrections have 5 bands, which are referred to by ROMRaider as A, B, C and D (with the 5th being Wide Open Throttle - WOT). The A band correction is only for idling - whereas the B and C bands are for light engine loads and cruising. The D band is usually enriched further as thats used for heavier engine loads and the transition into Open Loop Fuelling (i.e. ignoring lambda sensor feedback and only using the ECU fuel maps at higher RPM).
So - when you start the car its cold and in band A. Blipping the throttle forces it into band B or C temporary - followed by you setting off in the car on your journey. By the time you next come to rest the engine has warmed slightly and the ECU doesnt need to enrich the A and B bands as much - resulting in lower idle.
Last edited by The Trooper 1815; 16 February 2018 at 12:53 PM.
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