mine was doing this a few times. maybe the Idle control valve is clogged. i'll need to check this out. sometime it revs kinda high even when i'm braking (1500RPM)
My SC used to have an opposite problem. The engine is shut down when the A/C is off at idle. It was the ECU problem from what I've been told, but it's fixed.
More than likely the A/C compressor is locking up. WITH THE ENGINE OFF try to turn the front part of the clutch by hand. It should turn with slight resistance, if it takes a lot of effort or doesn't want to move you have a bad compressor.