I tried to search and couldn't dig to much up on this. I have a 87 gt pretty much stock i just bought the car and am new to the mustang thing and im bringing this thing back. The problem isn't constant and i haven't found anything specific linking to the problem. But it appears to be popping quite loudly out of the intake and sounds basically like pop corn popping and when this happens it falls on its face and stumbles quite badly . I run the highest octane fuel in it that i can. Could this be related to the egr valve in someway? . I have not checked the timing on it. And it only sounds like its popping from the intake its definitely under the hood. Any advice would be greatly appreciated thanks.