Recently my 2000 F150 5.4L 4X4 has been hard to start. It is turning over longer and sometimes has had gray smoke that smells like gas as if it were flooded. My fuel mileage has also taken a dump, down about 4-5 miles per gallon.Ii have replaced the IAC with no luck. I'm not sure exactly how the IAC operates, does the valve open fully when cold then slowly close as the engine warms? I am also down on power. Help? gas is not getting any cheaper.

I'm not sure if the new IAC is working correctly. When I hooked it up to 12v it barley moved. Does the IAC get 12v at start up and as the engine warms up the volts reduce allowing the valve to close?

 

This sounds like a classic case of injectors sticking open. Causing the black smoke, hard start, and bad mileage. Do some searching on how to test them. The IAC is controlled by the computer and opens and closes only during IDLE. Once you are away form IDLE it is not used anymore. As far as the valve movement inside I have not Idea, but it would not be a lot.

 

Get some new injectors or run several bottles of injector cleaner through Ure system