the reason it will surge is because you are letting un-metered air into the intake and when you apply the brakes it requires vacuum for the booster, adds more fuel then realizes this is too much fuel, cuts injectors then levels out again... It took me ALONG time to figure this one out. dont believe me? take your IAC off and seal the TB up with a block off plate in place of the IAC. Bet it wont surge anymore! They are activated by coolant temp to open and close for quicker warm up. When they stick then you get this surging up to 1400 RPM or so then a rapid drop in RPM's and the cycle continues as long as you are on the brake pedal!
