Take the following with a bit of NON -expert salt:
Could be faulty , but are you letting it run long enough to fully warm up for a bit instead of multiple restarting after a couple minutes run? After the install with engine off for 10 seconds, then the start & run for 5 seconds , the, Off for 10 seconds, then restart & run, I'd try letting it run after that until at least normal warm.
I doubt the continued restarting is helping until it has been further "educated" but I can see you might not want to let it do that if RPM continue to rise.
FWIW, I think I've mentioned when I replaced the IAC on my previous Jeep GC it took almost 15 minutes of driving for the control module to let the engine settle down to normal operation then it stayed normal. There were varying conditions including elevated RPM and a stall while driving before that point. Also foggy on this , but my IAC's instruction may have required disconnecting & reconnecting the battery at some point. Just a thought.
Keep in mind I expect the engine sensors are sensing/reporting odd conditions to the ECM during the learning curve (particularly engine voltage and Engine Coolant Temp and RPM, maybe the TPS), so it can take a while for the ECM to sort everything out and encourage everybody to play nice together. At least that's the way I prefer to conjure up the concept.
Did you by any chance pull or push on the pintle out of curiosity? ( It's entirely possible I might have done that, not at all sure. But it is a no-no and can temporarily or permanently put the IAC out of whack to use the highly technical term. )
Did you remove the pintle cap? As I recall & may be wrong) that is just a protective cap to be removed prior to install , but check the old IAC as to whether cap was on or off & definitely match that.
Also, generally IAC's can be adjusted in or out by screwing in or out the threaded pintle shaft, but they are supposed to be pre-set at the factory for specific applications and should NOT need that kind of adjustment. It's always just possible yours was not adjusted well ( too far into the IAC body, so throttle body IAC valve is not being closed off properly by pintle extension. I'm just a boater so am just throwing that out.
I just read in the Crusader 5.7L MPI manual, with a scan device the IAC position parameter would normally read ( at normal idle) step 20 out of a range of 0 (closed/ extended pintle) to 255 ( max air) step-position range. Yours could be different.
Sorry, I doubt any of that is going to be much help.
