How did you clean your IAC? And if you removed the IAC to clean it, did you also clean the orifice in the TB the IAC's plunger fits into? Crud in the orifice can make it hard for the IAC's plunger to seal properly which would cause a vacuum leak or even intermittent vacuum leaks.
Personally I prefer cleaning the IAC with it installed while the engine is running at idle rpms. When the engine is idling, the IAC is the sole source of air for the engine so as it draws in air, it would also draw TB cleaner in through itself cleaning both the IAC's plunger and the orifice. Raising the rpms will take the IAC out of operation so it won't draw cleaner in through itself so keep the engine at idle. When the engine dies from the cleaner flooding the IAC, that's no problem... just restart the engine. Not to mention that extra time the cleaner sits inside the IAC after the engine dies works to your benefit by giving it more time to work.
Generally speaking I try to get at least a third of a can of TB cleaner past the IAC to assure it and its orifice is clean.
Good T/shooting, I like that, and will do that... I have a similar problem coming to a stop...the higher idle (1200rpm) at first, then after 5 seconds at a stop, drops to 1000 rpm-ish...It showed up after I did the full mod of 4.0l onto a 2.5L manifold (shaved heads, O/size valves, hogged out intake to the 4.0L diameter)...confirmed no vacuum leaks; Replaced the IAC motor, TBS and MAP, just on spec, since it IS a '97...old and wonky, like me...
It all worked fine until the P1294 code popped up, after idling more than 2 min (stoopid train crossing)...but, even before that, I had a slower start, and when it did start, I had an ignition pop in my headers...otherwise, purrs like a kitten, good gas mileage and nicer throttle response (torque more than HP, but since the ecu controlls the engine curve response to the throttle, the HP performance would be similar...torque...that is from the engine)...
mind you, I had to make a gasket for the IAC unit (replacements not available...go figure!)...a wrong gasket material
could be a vacuum leak...gonna try the cleaner trick, and if no response, will pull my homemade gasket, and paint the stupid thing with a gasket maker, and see what happens...any ideas?