To test your fast idle valve, take off your intake. There is a hole on the inside of the throttle body.

When your car is cold, there should be suction at that hole. Put your finger over the hole to check. When your car is warmed up, there shouldn't be any suction. If there is, you need to either buy a new one or screw in the plunger.

You would use brake/carb cleaner on your IACV screens if they are gunked up.