1991 Ford Escort Won't idle all the time

I'm not sure if I listed the right cylinder size for my car; it's a standard 1.9 liter engine 5speed manual transmission if that helps. The first time I drive the car in a day it runs fine and idles all the time when I take my foot off the gas. If I let the car sit for an hour or longer, it is fine and idles as above. However, if I drive the car before an hour has passed it won't idle at all; every time I take my foot off the gas, it dies immediately and has to be restarted. The only way to prevent this is to keep my foot on the gas pedal when I stop. If I then stop driving it and let it sit for an hour, it will idle the next time I drive it. I've been told that it probably needs a new idle air control valve but I priced a new one and it costs $460.00 which I don't want to pay since the car is most likely not going to run much longer. I've had it 18 years, bought it brand new and generally it has been great. I had the head gasket and radiator replaced in 2004 and haven't had any major complaints since then.

My questions are: Is it defintely the idle air control valve and if so, what part of the engine would that be listed under in a repair manual? Can I purchase a used idle air control valve at a wrecking yard instead of installing a new one? How difficult is it to do the repair and is there anything that may occur if it isn't done by a repair technician?