1999 Toyota Rav4 Diagnostic Code P0505

Every first start every morning, I have to keep my foot on the gas pedal for about a minute to keep it idle (if start without pressing the gas pedal the engine will die), after that it start and idle fine all day.
If I park the car for a few day, it will be very difficult to start on the very cold morning (have to crank 8-15 times). About a week ago, the check engine light came on and went away after an hour of driving. My scanner showed P0505. IAC cost about $200, I don't want to replace until I'm sure it's the problem.
Any suggestion? Thanks.