This exact same thing happened on my ED, tho ford told me it was only ED's that suffered it obviously they were wrong. The idle up is controlled by the EEC. I took mine into ford and they hooked it up to a computer, adjusted the idle speed, and i haven't had a worry since. That was over 2 years ago.
White ED falcon, 2.5" redline zorst, pacemakers, 1 muffler, hi-flow cat, XH snorkel and K&N filter, 17" wheels, clear side and front indicators, king springs (low).