If its a diesel it could be the vacume pump. you can test this yourself. get into the car do not start the engine.now keep pressing the brake pedal until it feels stiff.now press the brake pedal while you start the engine you should feel the pedal pull down with servo assistance.The same applies to a petrol engine but there is no vacume pump on a petrol engine as it uses intake vacume for the servo.As your problem is intermittemt i would not think it is the servo.Hope this helps you.
Ras
January 2011
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