Rough idle after disconnecting battery

[bhoglan]

Hi Folks, it's me again.

So, this weekend I replaced my driver's side CV Axle as well as my Thermostat. Aside from learning that GM's alternator placement engineer is a sadist, I ran into some strange behavior when we were done.

The battery was disconnected so I didn't kill myself on the alternator. When I reattached the battery and started the truck, it had a rough/unstable idle that would dip down to almost dying and then jump back up. This happened both times (I had to rip it all apart again and replace the O-ring because the thermostat ate the first one when I torqued it down). The second time the truck actually died a few times. Both times it seemed to correct itself once the engine was well up to temperature.

Now, I assume that when the ECU loses power, it'll have to relearn certain values from the engine as it heats up. I'm not terribly familiar with ECU designs but I figured that a lot of the engine management values would be on non-volatile storage so they don't disappear when power is pulled. The alternative, I guess, would be for the ECU to have a battery inside it to keep the values when main power is pulled.

So, my question: Is it normal for a TB to act like a jerk after the battery has been pulled. If not, does the ECU have its own battery that I need to check? If not, what are your guesses?


Thanks!
Brian

[bartonmd]

Idle relearn. Normal.

[v7guy]

Yup, normal

[PROSPHOTO]

I would speculate that the idle relearn is more noticeable the dirtier the throttle body and IAC motor are... Something that needs to be cleaned routinely on these vehicles.

[v7guy]

There is no idle air control motor on the I6, fortunately cleaning those things are behind us!

[PROSPHOTO]

My bad, the butterfly itself acts as the IAC, carbon build up around the edges where they contact the inside of the TB would yield the same symptom

[bhoglan]

Ok thanks for the advice. How do you folks clean your TB's? Are we talking a seafoam kind of thing?

[Rickalicka18]

Its been done before. Check youtube for it. I believe some guy did a tutorial on it using his trailblazer.

As for other ways to clean, that's all I have heard of for cleaning carbon build up

[TBYODA]

https://youtu.be/VdvgsaDmkac