On my 2.0 Auto the rear silencer has 2 outlets, one of which has/had a vacuum operated "flap" inside it. As far as I'm aware this flap has not operated since I've had the car. Silly questions are: What does it do? and as mine is stuck wide open does it affect the way the engine runs? Fitted a new inlet camshaft position sensor today at work as it was quiet and she has not run so well since I've had her.