Boosting for no reason

[Lostfarmboy]

I am new to rawze.com. I just purchased a 2010 Pete 386 with a isx 871. I did the egr tune-up and set the overhead before putting it to work but now it is boosting to 20ish pounds when a small amount of throttle is applied at lower rpms. If I let off it then get into it again it doesn't do it. I'm confused.