I've been asking and trying to figure/find out why my car is idling badly, trying to die when idling and backfiring when down shifting. Well I finally had my mechanic run a test (I forget the name of the thing) thing on my car. I had to leave so my friend wrote stuff down for me. Now I need help on trying to fix this problem and understand it. :/

The Note:
Code 327 EGR Signal to low isn't hooked up
Code 539 ac/defrost

That's all my friend wrote down and he said my guy reset the computer or something. I kind of want to buy one, they're just a little computer, kind of like a laptop. LoL

1995 Ford Mustang GT 5.0