As the vacum that works the brake servo is obtained from the inlet manifold via a pipe, if the pipe has a hole in it or is loose this could be causing your problem by weakening the petrol/air mix in the manifold causing the engine to stall.
Depending on the type of fuel system on you car it sounds like the stepper motor or idle contol vave is playing up this could be caused by a split pipe or the part is gunked up inside or its nackerd..It lives very near the throtle body on it or next to it on the inlet manifold. would be worth taking it of and cleaning it with some carb cleaner or somthing like it the re fit it. Once you have fitted it you need to reset it by disconecting the battery for a few mins then re conect and fingers crossed no idle prolem. if you do fit a new one or a second hand one you will have to re set it by disconecting the battery.
Hi my guess is the tdc sensor try a search and see if that sounds like your problem some times when you have a diagnostics test done it will only find a fault if a sensor is telling it so and sometimes i believe the tdc sensor can be intermittent so it might have just been fine at that time Donald