I know I'm agreeing with someone hear......I have had many motors idle well with the muffler pressure line off, advancing the throttle open is where the problem comes in. My instructor 25 years ago said if a muffler came off in flight don't adjust the throttle......just set up for landing and bring her in and most times she won't deadstick at a constant throttle setting......He was right I have landed more than a few times with out a muffler(no pressure) and the engines stayed lit all the way to landing/Idle, but don't miss the landing cause throttle up (quick pressure change)go arounds are probably not going to happen.