What causes an engine to backfire lean or rich?

[@alikdouh369]

My backfire/pop only happens when I revv on 4/5 rpm but sometime when I drive it will happen but I like to have it daily basis everytime I downshift on 2 or 1 gear how can I fixed the issue

[@monsieurixe6790]

I don't get it... why does the 100% OEM engine in my Acura ilx 2017 makes backfires since 1st day. I didn't know this was a problem.