Rough idle after battery disconnect

Started my truck up this morning, CEL and VSC light lit up. Looked on the forums, sure enough my gas cap was loose. During my lunch, I went to autozone to have them scan my truck real quick and make sure that’s the only code on my truck. After making sure the code was for a loose gas cap, I disconnected my battery for a few minutes, reconnected and turned the truck on. Drove for about 40 minutes, rough idle around 300-500rpm at stoplights, occasionally died out a few times. My question is for the people that have disconnected their battery and dealt with a rough idle once driving again, approximately how long did it take for the idle to go back to normal, given the truck has to “relearn everything”? I’ve read some people say it takes a few days of driving for it to go back to normal, but I drive 3 miles round trip everyday for work, never getting above 50mph, so I don’t know if that’ll affect the time it takes. Picture is my rpm at a stop.

 

Clean your Throttle Body, that should take care of your problem. As it get's dirty over time the computer adapts by opening the throttle more, when you disconnect the battery the computer "forget's" it's adapted position and goes back to it's base value, if the throttle plate is fairly dirty this causes low idle and or stalling until the computer relearns it's adapted values.

 

Depends on how much modding you've done that would require the factory tune to accommodate for, with only driving 3 miles at a time I can imagine you might have some sludging as your engine doesn't get hot enough to burn off any condensation moisture.

I would check your PCV valve operation.

I let my truck idle for at least 20-30 minutes before driving it to relearn a stable idle after disconnecting the battery and it takes about a week of driving to relearn me and the mods.

I drive 30 miles to work one way and it's not uncommon to put 100+ miles in a weekend so with your limited travel it might take a good while unless you cruise the island perimeter loop for a day.

 

Clean the throttle body

 

Cool, thanks for explaining all of that. I’m guessing mines is pretty dirty then. Had the truck for a little over a year and I’ve never cleaned the throttle body or MAF, so I’m only guessing it’s been gunked up for a while.

No engine mods whatsoever. I’ll probably go outside in a bit and let my truck idle for 20-30 minutes, then go drive around for another 30 to see if that does anything before I go clean the throttle body. I’ll probably have to drive around the island this weekend then, it’s about a 120 mile trip so maybe that’ll do it. Thanks for the advice.

Definitely on my to-do list now, thanks for the tip.

 

Just be aware if you let it relearn it's "dirty" throttle body values and the go clean it you may get a high idle for awhile till it relearns the "clean" values.

 

Make sure your ground connection is tight