Idle and backfire problem

[Charlot]

Thanks for the advice

Update.

The check engine light wasn't working so I changed it because the codes wouldn't appeared without it.

Code P1691 : Check Engine Malfunction Indication Light (MIL) - Open Circuit
---> We just changed the light and it's ok now.

Code pending P0102 : Mass Air Flow Sensor - Below Lower Limit
---> The MAF sensor has been changed... could it be something related to the MAF that brings this code ? What does it mean : the sensor is not working properly or the sensor detects something is wrong ?

I erased the codes to see if they would come back when I start the engine. Nothing happened and the it ran really fine ! Seems like an intermittent problem...

Any clues on what the problem is ? Oil separater ?