Because your vehicle's engine is electronically controlled by a computer, some control conditions are maintained by power from the battery. When the battery is disconnected, a new battery installed or a tune is loaded, the engine must relearn its idle and fuel trim strategy for optimum driveability and performance. The process for this is as follows:
1. With the vehicle at a complete stop, set the parking brake
2. Put the gearshift in P (Park for Automatics) or Neutral (for Manuals), turn off all accessories and start the engine.
3. Run the engine until it reaches normal operating temperature.
4. Allow the engine to idle for at least one minute.
5. Turn the A/C on and allow the engine to idle for at least one minute.
6. Drive the vehicle to complete the relearning process. The vehicle may need to be driven for 10 miles (16 km) or more to relearn the idle and fuel trim strategy.