Does the IAC act as the choke on the fuel injected F 150? I know it varies the air amount when idling. What part does it play on crank up?I know the system is in open loop when cranked. Can the IAC cause harder cranking but still good idle. I am trying to trouble shoot another Ford and better understand the system. Appreciate any imputs on where to go for more info in this area.

 

I believe that the main choke devise on a fuel injection motor is the coolant temperature sensor. it tells the computer that the engine is cold and then the computer increases the fuel suppy and probably closses the IAC valve.

 

the IAC is the ONLY way the engine gets air at idle. If you take off the intake hoses, you'll see the throttle plates will be competely closed. (with engine off) It's not like the old days!! Control of this IAC via the various sensors, has 100% control of the idle speed. One way to check this is to pull a vacumm line off and the engine will speed up a bit.(@ idle.) As the engine warms up, the IAC adjusts the air by the slider valve which in turns adjusts the speed. Of course the computer is the brains of the hole thing! Interesting trivia- one of my repair books says both stoplite bulbs must be working. I recon the ol' computer senses when your stopping, and the amps thru the brake lite bulbs??? sounds crazy.....glad to be of some help...

 

Yup, it's the only way it gets air at idle. You'll know when your IAC won't open because it'll idle reeeaally slow, and sometimes stall under load at idle (like turning the wheels all the way to the stops and putting a load on the P/S pump).

Steve