Idle Speed After Battery Reconnection

The copper terminals on the battery are almost completely digested on my 2009 and I want to swap them out for lead terminals but there is one problem with that. When the battery is reconnected after being disconnected, the idle speed drops to 500 rpm and only over a period of a week in commuting service does it come back to normal. Apart from using another supply to maintain voltage during the changeover, is there a way of defeating the stupidity programmed into the CPU? As it is, this is dangerous to drive once the battery is reconnected.

Standard relearn procedure once the battery is disconnected is to turn off all the accessories, lights, etc. and reconnect the battery.

Start the car and just let it sit idle for 10 min.

This allows the ECU to relearn idle and it should be fine after that.

If it is not, then something else is wrong and needs to be addressed.

Yeah, it shouldn’t take a week. If the long first idle doesn’t get it try a couple of short drives with a couple of key cycles. If the idle is so low that the car tries to die there may be other issues like a vacuum leak.

I had the same thing happen, driving did not help, what did help was the key on let sit , then start and idle you can look up how to do it " throttle body re learn"

 

The first time it happened my shop forced a re learn with a scan tool.

 

The second time I did the manual re learn

 

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Just a follow up and thanks to all who responded. I have a small 12 volt solar panel and I decided to use that as a power source to supply the necessary dark current to retain memory when I swapped out the positive battery terminal. I cleaned and reused the negative terminal as it was not a problem and it was either silver-soldered or spot-welded to the cable. I used a marine battery terminal with a lead body, steel screw and brass wingnut to replace the copper terminal that had fractured in two places and was not making contact.

 

The solar panel was almost good enough and it was a cloudy day here in the Toronto area. I had to bore out the two positive cable terminals to fit the battery terminal but it all worked. The voltage never went to zero in the car but not everything was preserved. One of the radio presets was preserved but not the rest. The clock was about twenty minutes out from where it had been. But the idle speed was at 650, a welcome relief from the 500 it would have been with no voltage on the system, so this is one in the win column.

 

 

The lead terminal on a lead battery post means no more blue copper salts all over the place. The old terminal had fractured in two places so it was never going to work longer than a month and I would not want to be outside in the weather we are going to get a month from now. I used the alternator screw for the positive connection and one of the grounds on the intake manifold for the negative connection of the solar array. The red cap on the alternator terminal has a push-to-release tab on the battery side so don't manhandle it.

 

I'll save the other battery terminal for the next car.

Standard relearn procedure once the battery is disconnected is to turn off all the accessories, lights, etc. and reconnect the battery.

Start the car and just let it sit idle for 10 min.

This allows the ECU to relearn idle and it should be fine after that.

If it is not, then something else is wrong and needs to be addressed.

 

I like to add one more step to a battery reset just fyi - insert key and turn the ignition to 'on', let the cluster cycle, then crank and let idle for awhile.

 

I like to do this after it's sat for an extended period too. I believe it maybe primes the fuel lines?

 

If it's sat for a really long time, you can also prime the oil by holding the accelerator pedal to the floor and cranking. The motor will not turn over if you keep the accelerator down.

Edited December 12, 2021 by BoozeRS05

I like to add one more step to a battery reset just fyi - insert key and turn the ignition to 'on', let the cluster cycle, then crank and let idle for awhile.

 

I like to do this after it's sat for an extended period too. I believe it maybe primes the fuel lines?

 

If it's sat for a really long time, you can also prime the oil by holding the accelerator pedal to the floor and cranking. The motor will not turn over if you keep the accelerator down.

 

each cycle of the key primes the pump. if the car has been sitting awhile, cycle the key 4-5 times before starting, i also wait for the cluster sweep to finish. holding the throttle to the floor will allow the motor to turn over, but not run. should take 30-45 seconds for the oil pressure light to turn off.