Greetings Mike, and welcome.
If the IAC valve or ports were carbon coated, the next step is to clean out the carbon buildup from the throttle body and give the throttle plates a thorough cleaning.
This link may help:
What causes an engine to stall at idle but run fine over 1000 rpm
(I prefer to use regular throttle body cleaner, budget-brand.)
The only "trick" here is to limit, as much as possible, the amount of cleaner you introduce into the engine, as dumping vast amounts of cleaner into the intake manifold will ignite when you start the vehicle - Not good for the O2 sensors in the vehicle.
So, with the throttle plates at Wide Open Throttle (WOT), using a cloth rag (an old cotton T-shirt works best) inserted in the throttle body / past the plate(s), spray the cleaner so the rag soaks up all / the majority of the cleaner. *Do not use paper towels, etc: these can catch / tear on the throttle plate and fall into the intake manifold - then you'll have another issue to deal with..*
Use a soft bristled toothbrush to clean both sides of the throttle plate(s).
Shoot some cleaner directly on or dip in a cup of cleaner and scrub both sides of the plates gently until the carbon is removed, then wipe with the rag. Be as sparing as possible w/ the cleaner & Repeat as necesssary.
If heavily coated it will take several cleanings to loosen up the buildup: just take your time with it, eventually the carbon will loosen to where it can be wiped off.
If your throttle body has (2) plates, just do one side at a time.
After the throttle plates are nice and clean, and the IAC is cleaned up, try hooking back up, see if there is any improvement.
As to "why" the throttle body is building up carbon, most common causes are
Failing and/or biased upstream O2 sensor,
a dirty MAF sensor,
incorrect data from the engine coolant temp. sensor to the ECU.
All of these will make the motor run rich -> build up carbon.
If you haven't already, consider signing up at the kiatechinfo.com website (see my sig) using Internet Explorer: there you can see the fuel system troubleshooting diagnostic chart for your vehicle, which includes the indicated resistance values for the coolant temp. sensor for testing it.
While I don't generally recommend the use of "additives", adding a fuel system treatment 1 or 2x a year to clean the fuel system & injectors is not a bad thing to do.
I prefer to use a product called SeaFoam - I add about 1/3 can to a full tank of fuel every 6 months or so (just follow the recommendations on the label).
There are others who use it directly in the engine for cleaning, that's one of the recommended uses (you'll see this if you search the product on the internet.)
Given the amount of mileage on the engine, I would -not- recommend
adding any "additive" product directly to engine oil: keeping up with a fresh oil / filter change using a quality oil regularly is really the best way to maintain & prolong motor life.
Some fans of SeaFoam use the product directly in the Intake Manifold by ingesting it through a vacuum hose at the intake manifold, turn off the motor, let sit, then start and run to loosen carbon buildup. This does work & has some merit, but again, depending on how much of the product used, I would recommend an oil / filter change immediately after doing this procedure, to remove any SeaFoam product introduced into engine oil while doing the "fogging" procedure
(Apologies for the long "SeaFoam" digression, just want you to have accurate info. if you decide to use.)
Sea Foam | How to Use Sea Foam Motor Treatment
Good luck, and hope the info helps.