Being an auto has nothing to do with the performance output of the engine. You'll still get the same power from the chip.

Also, just from my bmw side, i just put an ECU in myself and was not hard to do at all and it is a significant difference in power vs. stock chip. You would have to look at the higher end chips to actually get some power out of it. I'm not sure how much you want to spend on a chip, but if you can get an ACTUAL one from like mugen or one of the major car tuners you could get some good power out of it.

On gas mileage, the chip will not affect that, it just depends on you drive the car with the chip in it I wanted to floor it off of every light cause it had so much more power, so its all a drivers thing

Good luck, if you're not willing to spend much money on mods, that the guys advice and use it for repairs to keep the car on the road.

~Andrew