what is wrong with my car? what do i need to replace to make it run better?

Does it have a check engine light and when was last tune-up??

Sounds like lean misfire-check the fuel pressure if its within specs-start here and also go to this link: https://www.2carpros.com/articles/engine-backfires-while-running and https://www.2carpros.com/articles/engine-misfires-or-runs-rough

it just had a tune up, the check engine lite comes on only when the problem happens then goes away. we know it is running lean but dont know what to fix to stop it from runnung lean

Lean fuel condition could be caused by one of the following below:

1.Vacuum leaks

2.EGR and PCV valve.

3.Low fuel pressure.

4.Dirty fuel injectors.

5.Mass Air Flow Sensor.

6.Oxygen Sensor.