I think a custom chip is as good as the afc. I do have some dyno info on this that I have not shared yet. I now have 127 dyno runs with an afc hooked up and I can tell you this. If you reset your computer or battery dies, turn your afc back to 0's for a couple of days. The computer has to relearn it's old a/f code before the afc can correct it. I have reset and left it lean out mode and the car goes lean. I have also reset with the rich setting on and the car will then go rich and you will have to lean out the afc. It will however hold the air fuel as long as there is no reset. I have gone months and gone back and the air fuel mapped beautiful, as long as I didn't reset the pcm. I have a theory that if you dyno and get the #'s for your current set up and then have to reset and let the computer relearn you should be able to put the same #'s back in and be the same. I haven't proven that part yet due to other projects I am working on. Now remember I am returnless so the pcm is controling the fuel not a fpr so it may be different for cars that are not returnless.
Bottom line-afc works great and gives great gains across the rpm band. So will a chip. They are both effective, just one you need to pay more attention to and the other you just pay more on.
