Is the high idle only during start up?Get your engine warm,let the idle settle to normal and unplug the iac while the motor is idleing.Leave the iac unplugged and restart the motor....does it still have a high idle?If it does then it would confirm that you have a leak or bad seat in the tb. or intake manifold.
If it idles normal now after you disconnected the iac then I would suspect bad iac or bad latch circuit.Which is responsible for positioning the iac for start up