Has anyone checked if the IAC valve is even moving in the real world? It should seat itself and open back up once upon KOEO conditions. Another problem is mismatched pintle styles that do not seal properly against the throttle body idle passage. They all swap. Try plugging off the inlet port to the IAC, and see if the rpm drops.....use a rubbermaid glove or something, whatever works. If no change, then remove and plug off all non-critical vacuum ports, remove the pcv valve from the valve cover, start engine, and block off the pcv vent on the other valve cover. Now block off the pcv valve grommet in the remaining valve cover with your hand, and see if the crankcase still has vacuum. If it does, then you have an intake gasket problem.
The only other thing is setting the tps to exactly .50v at closed throttle, and have the timing set to stock timing at idle (on the chip, too), but I suspect this has already been done.
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