By what method did you happen to check for Vac leaks? I have found in the past that the air distribution hoses along side the valve covers and connect to each injector can sometimes be hard to diagnose vac leaks on. They get brittle and crack, thus letting air bypass the ICV and give you the above symptoms when the engine warms up. Did you check the crossover vac tube under the upper intake below the FD that connects the air distribution tubes together? I know you mentioned above that you have checked for vac leaks but I would try one more time. Did you check the voltage at the ICV? Use a unlit plumbers propane torch to check for vac leaks around the Intake and injectors.