idle speed

If the brake pedal is high and hard you bay have a vacuum leak at the booster, this will also effect the engine idle, have the booster checked or you can do it quickly by pumping the brake pedal with engine off till the pedal is very hard, hold pedal down and start engine, brake pedal should pull down with pressure applied, if not the booster is faulty or you have a vacuum leak in the booster supply line.