I'm sure someone will correct me if i'm wrong, but I think it cycles air into the exhaust to burn off any unburned gas, in an effort to have cleaner emissions, which is basically similar to an exhaust leak. I did the pair valve removal after clayton and I still get popping on decel, sometimes it's a little pop, sometimes a goddamn gunshot. pisses me off pretty bad. worst is when I'm flying down the highway at 80, 85 (more like 75 w/ speedo error) and traffic in front of me slows enough to roll off the throttle, but not necessary to brake.... I roll off the throttle and BLAM fluttler flutter flutter flutter BLAM! flutter flutter... so I pull in the clutch at 80 and just feel slightly less stupid.