idling low

My battery just went out after 4 years. I used a jump box to start the truck and drove it down to the auto parts store had them test the alternator and battery which showed the alt was good but battery was bad. I replaced it but now the truck idles really low. I never really paid much attention to what it idled at before but now it runs around 400-500 and can shake a little when it gets real low. I'm not sure what would cause this as all I did was replace the battery? But I definitely don't understand these newer computer systems.

 

It is normal to have an idle issue when the battery is disconnected and reconnected. It is in a learning mode for the ECU. Take it out and drive it a bit and it should straighten out.

 

Take the intake box off and clean the throttle body. When the battery is disconnected and values reset the throttle plate closes all the way. When the tbody is dirty it has a hard time idling until it relearns (now learning that a dirty tb is normal)