Hello, Code P0102 is Maf low input. This code can mean more than just a MaF problem. It is the computer saying that the engine is getting more air than the maf is reading. This can be a clogged intake, a leak in the intake piping, or another airflow issue. Start by checking your intake piping for obstructions or damage. Focus on the area after the maf. If you don't find the issue
If you don't find the issue in the intake pipe, check all your vacuum piping. If you don't find the issue let me know.
what about the backfire and it ran fine before the maf sensor was replaced?
Backfires can be caused by any fueling issue; too much, or too little and you can have backfire situations. Are you sure that it is a backfire and not a misfire?
Also, they may have reset the PCM to clear your code after replacing the maf. This will also reset the fuel trim adjustments that your car had learned. This may have uncovered an issue that had been covered up by the cars adjustments.
I already knew what po102 is, what about the backfire and running better when warm
car is running fine . I think it needed to re-learn some settings. Thanks for your suggestions.