Idling fast on 1997 Toyota Corolla

My Corolla starts idling fast (1,600rpm) for 15- seconds and than dips back to normal for about 5- seconds before rising back up again. The dealer thought the MAP sensor, but that didn't fix it. The control unit is causing the fast idle, but I don't know why it feels it needs to compensate

Asked by for the 1997 Toyota Corolla
The idle air control valve (IAC) gives a little trouble on some Toyotas. Usually when it gets carboned up the little drum that rotates (and allows air to bypass the throttle butterfly) binds up and causes the engine to stall on cold starts in the morning. I am wondering if the valve is sticking or someone has compensated by adjusting the idle speed screw. Toyota dealers usualy want to replace the valve but I and many of my friends that work on Toyotas have success cleaning the valves. The IAC valve and idle speed base setting has to be correct for the idle speed to be properly controlled by the fuel injection computer.