with tuning you will always have gains, however I'm not sure if there is a correct wiring diagram for the mafterburner on an i4. Also you need t know if your a maf based car or map based. If its map based then a mafterburner will not even work
The MAFTerburner should work find provided you can get the pinouts for the unit. Chances are it has a RPM tap, MAF in and out, and power and ground. Fairly simple to wire up in the engine bay. As long as you can get it reading the correct RPM then you should be good to go!