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I actually ran it without one to start because I didnt think I needed one, but the pcm uses it with brake pedal sense to adjust the idle speed. The car ran ok, but on closed throttle decel it would stall intermittently, without brake pedal sense it kind of thought it was doing a stall speed test all of the time! This is my first efi swap so I am learning as I go.



The PCM on some car looks for a reduction of speed along with the brake pedal input to see if the car is slowing down.

When it sees these two events it starts raising the idle speed to prevent the car from "flaming out" when coming to a stop.

You can get around it to some degree by raising the base idle speed (usally hiding under an anti-tamper cap) a half turn or so.

This will cause more air to come in at idle around the blades rather than the AIS motor passage and help the problem.