I have an 84 Fiero which ran absolutely terrible when I got it, it now runs 100% and gets something like 28 mpg even with all the hills here and doing 3000 rpm.
The IAC valves are common, as JMTUT said get them on rockauto, they're even on sale right now.
Make sure you didn't break the threads in the throttle body. I have a disassembled throttle body I could send your way if you ruined the threads although you'd need to rebuild it.
The first thing is the ECM temperature sensor, this is practically a must if you can't test the current one. Unless the car sat for a very long time I wouldn't worry about the injector right now as they're very durable.
I'd say both of you should change your spark plugs, wires, distributor cap and rotor, and ignition coil. Weak igniton = incomplete combustion, gives similar signs of running rich. If it's the original coil you'll need to grind off the rivets. If you're unfamiliar with it the cap and rotor is safe to do, you can't mess up the timing. Mark the wires by their position, they must go on the new cap in the same order. Also when you change the spark plugs blow compressed air at them before removal to clear out any gunk and rust. DONT skip this.
You may also have incorrect timing on the distributor although if this were the case you'd likely have difficulty driving it at all especially up a hill.
Here's a list of what I've done on my engine to get it up to 100%:
spark plugs, wires, distributor cap and rotor
ignition coil(still had the original)
thermostat and ECM temperature sensor(in the filler neck)
fuel filter
throttle body rebuild
replaced all vacuum lines
PCV valve, breather filter(circular thing on top of valve cover)
valve cover gasket
disconnect vacuum lines from cruise control(I never reconnected it)
disconnect vacuum lines from charcoal canister(this you should reconnect when its running properly)
MAP sensor, IAC valve
intake manifold gasket
engine computer(ECM): these can degrade/fail but my problem was that the previous owner put the wrong one in! they put in the ecm from an 85 automatic into my 84 manual.... it really didn't like that. moral of the story, make sure you have the correct ecm.