Based on the OP, mentioning 1997 5.7L, I went to RockAuto (easiest place to look up a part without having to "add a vehicle to my garage" like AutoZone) and since this is an RV forum chose "Express 3500."
That netted TBI and an IAC valve that looks like
That IAC looks like the one on the 1996 5.7L EFI in our boat. I replaced it because about one slowdown in 100 or more, engine'll quit. Mechanic with a scanner (different than automotive because of MerCruiser's adaptations of a few systems) has never found a clue. Cleaned IAC a couple times before I ordered one from BoatFix and swapped it. Now it quits one slowdown in 200 or more but I don't think the IAC really addressed the problem. As I recall, the TBI was held with Torx Head screws, so check before you go after it.
Still, if IAC has never been at least cleaned (I used Throttle Body Cleaner, but the manual says NOT to clean one but replace instead), the OP might find it would help. The IAC was not as gummed up as were the passages it controls. There's also Throttle Body Service (cleaning) that might help here.
