Info to Share - Toyota Yaris Forums

barryware · 12-12-2011, 10:24 AM

I replaced my water pump 2 weekends ago.. In doing so, I disconnected the battery to remove the alternator..

Once the job was complete (3~4 hours), I started the car.. took it for a quick drive to heat it up, get all the air out of the cooling system, and top off the radiator and reservoir tank after it cooled.

I noticed that for a while, the car would barely idle.. I have a scanguage II and the car would idle about 430 ~ 450 rpm (normal idle is 600~650 rpm).. It shook and rattled. To keep it lit at the stop lights, I would put it in neutral and rev it a bit. After a few miles, it was better but still not running right. I wasn't sure what was going on at the time but after a couple of days driving the car.. everything straightened out and the car never ran so well or smooth.

Unfortunately for me, the new water pump was defective (new.. not a rebuild). It was leaking around the shaft. I had to replace the water pump again last weekend.

The same thing happened in regards to the car not idling right, not shifting right, etc. after putting it back together and running it. Now two days later (maybe 100+ miles or so between test driving it and a trip to the office), it is again running and shifting as smooth as silk.. Maybe even better than when I first bought the car new.

I am pretty sure that the computer(s) in the car "learn" as they go but I was not aware that they would "forget" if the battery was disconnected.

I am going to make it a scheduled task to disconnect the battery and let it sit for a few hours a couple of times a year. I might suggest others do the same. As said, my car has never run so well & smooth and I am sure it is not my imagination.

2007 USA HB.

CTScott · 12-12-2011, 10:39 AM

Disconnecting the battery for long enough to discharge the capacitors (> ~30 seconds) causes the ECM to reset the short term fuel trims.

With my Supercharger, I do it about once a week to prevent the ECM from learning how the extra fuel from the Blitz fuel controller richens the AFR. If I don't reset it regularly, the ECM adjusts the fuel trim enough that I starting running lean.

mr_miles · 12-12-2011, 01:05 PM

Oh wow, i had no idea they could "learn" like that. going to try this on mine and see if anything changes, lol.

rick996 · 12-13-2011, 09:33 AM

Thanks for the tip barryware. I'm going to give it a try.

12-12-2011, 10:24 AM	#1
barryware Drives: 2007 Yaris Liftback Join Date: Sep 2006 Location: Chicago Posts: 129	Info to Share I replaced my water pump 2 weekends ago.. In doing so, I disconnected the battery to remove the alternator.. Once the job was complete (3~4 hours), I started the car.. took it for a quick drive to heat it up, get all the air out of the cooling system, and top off the radiator and reservoir tank after it cooled. I noticed that for a while, the car would barely idle.. I have a scanguage II and the car would idle about 430 ~ 450 rpm (normal idle is 600~650 rpm).. It shook and rattled. To keep it lit at the stop lights, I would put it in neutral and rev it a bit. After a few miles, it was better but still not running right. I wasn't sure what was going on at the time but after a couple of days driving the car.. everything straightened out and the car never ran so well or smooth. Unfortunately for me, the new water pump was defective (new.. not a rebuild). It was leaking around the shaft. I had to replace the water pump again last weekend. The same thing happened in regards to the car not idling right, not shifting right, etc. after putting it back together and running it. Now two days later (maybe 100+ miles or so between test driving it and a trip to the office), it is again running and shifting as smooth as silk.. Maybe even better than when I first bought the car new. I am pretty sure that the computer(s) in the car "learn" as they go but I was not aware that they would "forget" if the battery was disconnected. I am going to make it a scheduled task to disconnect the battery and let it sit for a few hours a couple of times a year. I might suggest others do the same. As said, my car has never run so well & smooth and I am sure it is not my imagination. 2007 USA HB.

12-12-2011, 10:39 AM	#2
CTScott ULTIMATE View User's Garage Drives: 09 5dr LB, 2x 08 3dr LB Join Date: Oct 2008 Location: USA, CT Posts: 13,460	Disconnecting the battery for long enough to discharge the capacitors (> ~30 seconds) causes the ECM to reset the short term fuel trims. With my Supercharger, I do it about once a week to prevent the ECM from learning how the extra fuel from the Blitz fuel controller richens the AFR. If I don't reset it regularly, the ECM adjusts the fuel trim enough that I starting running lean. __________________

12-13-2011, 09:33 AM	#4
rick996 Drives: 2010 5 door hatch w/5 sp man. Join Date: Jan 2011 Location: Coventry, CT Posts: 160	Thanks for the tip barryware. I'm going to give it a try. __________________

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12-12-2011, 01:05 PM	#3
mr_miles Drives: 2013 Yaris Join Date: Oct 2011 Location: Portland, OR Posts: 914	Oh wow, i had no idea they could "learn" like that. going to try this on mine and see if anything changes, lol.