I heard a rumor.

The rumor says that if you disconnect the battery on your Tacoma that it may not idle correctly upon reconnecting. In fact it may need to be re-taught to idle? Any truth to this?

 

I love gossip

 

It's true on older models that have dirty throttle bodies.

There's 2 ways around it, clean the throttle, or let the key turn on without starting to allow the throttle zero position to register once the battery is reconnected.

Cleaning the throttle and MAF are good ideas to do and it helps prevent the low idle.

 

Yes, disconnecting the battery clears many learned values including idle airflow compensation.

If the throttle body is clean you may not notice a thing but if it's dirty it's not gona idle right until it relearns which may take a bit.

Best to keep the throttle body clean.

After a battery disconnect start the truck and allow it to idle until it gets to operating temp (idle learn on these isn't enabled until coolant temp goes above 174F).

 

Lured by title. Disappoint.

 

My truck starts then immediately dies the first time I crank it after having disconnected the battery. It has done this as long as I’ve owned it, but it always surprises me. The second time I crank it it runs fine. And yes, I keep the TB clean.

 

I have a 2013 2.7 auto. The throttle body is clean. If I disconnect the battery, there is a relearn period where the idle is funny - sometimes almost wanting to die at the stoplight for a while.

I don't remember where, but some time ago, I read to run the engine after reconnecting (it may die the first time you start it), but just let it sit there idling. It will go through a few minutes where the idle changes a bit, then after about 2-5 minutes (after it warms up a bit), everything miraculously smooths out and you're good to go.

Has worked every time - at least for me.

There is also a process in the service manual where you do a series of idling, acceleration, hold a certain speed, etc. for specific periods of time and it sets the relearn. I don't remember how long that process takes.

 

Yes, this is true for almost any vehicle made. Once you disconnect the battery all learned values in the ECU are reset to factory settings and it needs to relearn the specific parameters for your vehicle. Drive it for 10-20 miles or so and it'll have re-learned most of it. Also if you do this just before emissions testing you'll need to drive it long enough for all the sensors to fully reset. If you live in an emissions state.

 

They make "memory saver" devices you can use to retain pcm power while changing a battery, usually through the cigarette lighter port (accessory charger)

Sometimes I'll use a positive terminal in the fuse box or the pos terminal on the alternator to connect a jump box.. that keeps memory alive while changing a battery. Just be careful you don't arc something with a wrench while doing it

Subarus were terrible for this a few years back

 

Out of curiosity, I searched through my FSM and found the section under initialization. Note, this is for the 2TR-FE, so not sure if the 6 is the same.