You could clean the IAC, but it might be normal. This fuel system is designed to hold rpms when shifting. When you shift into N going downhill, the ECU sees a VSS signal, and maintains a higher rpm because that helps you shift into gears. Once you stop, it waits a few, then drops the idle to N speed.
Letting off the gas going downhill--- um, the idle will stay up then because the car is in gear. Fuel is cut off, but the engine will spin at the same speed because the wheels are turning the engine.
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Originally Posted by the user formerly known as ZX3_Chick
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