@Gdizzo
If 3000 rpm upon start-up is frightening or of concern, one might try restricting the air flow a bit by reducing the size of one of the holes allowing airflow through the IAC. I can't speak with knowledge of the 4.6L IAC, but the old 5.0L as used in Mustang, had holes about the size of a dime, call it 5/8 inch diameter. Area about 0.3 sq. in. If reduced to 1/2 inch, area = 0.2 sq. in. That's 30% less. I'd press a suitably-sized washer in one hole, having the appropriate hole size, and see what happens.
Here's how Ford's start-up scheme works. Upon cranking the engine, IAC is opened fully, allowing max. air flow. Upon firing, PCM detects the quick increase in rpm, and immediately closes down the IAC while it reduces injected fuel richness, the two being controlled to allow eng. rpms to drop slowly back to acceptable level. The drop-down is dependent on air and eng. coolant temperature, so it takes longer in Chicago in winter than in the Desert where I hang out.
I hate the sudden speed-flare, as they call it. Mine goes to 2200, I'd try my scheme above, but can't: NO IAC! Not a damned thing I can do about it, except the "hold pedal to floor" thing, which remains to be tried. imp
