ok efi gurus, someone explain the duties of I.A.C.


cammeddrz

cammeddrz

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not on any one specific engine or efi system. but what does the intake air control do? and how and when does it work?
 
With the throttle closed it controls the idle by moving a valve in or out to give the engine the proper air. The throttle position sensor tell the computer when the throttle plate/butterfly is closed. the O2 sensor and engine temp sensor tell the computer how much fuel the injectors deliver. If you have cleaned or changed any of the sensors you need to reset the computer by disconnecting the battery for 1/2 an hour and then run it for a couple of warm up cycles for the computer to relearn the new values. I found on my jeep the throttle plate shaft is a little loose and by opening the butterfly a little helps on startup especially after it sits for 45 mins or so but cold starts she fires right up. If you adjust the throttle butterfly you should reset the computer and start fresh with new values.
 
and just for the record,it's idle air control,not 'intake'.
 
The butterfly plate (valve) closes when you take your foot off the gas pedal. The IAC then opens to keep the engine running at idle, based on inputs from the engine sensors. When you accelerate, the IAC closes almost all the way and lets the butterfly plate operate air input and engine speed.

If the IAC is not working properly, the engine will surge or not idle at all.
 
got it!
 
It also works at start up. In many cases a faulty IAC will keep the engine from starting at all if the gas pedal isn't pushed a little to allow air in.
 
adsm08 said:
It also works at start up. In many cases a faulty IAC will keep the engine from starting at all if the gas pedal isn't pushed a little to allow air in.
Click to expand...

and when you let off it can stall thus cause of much angst and a small dent in a fender
 
Earl43P said:
Steering got stiff, the brake pedal got harder to push, yep. I can easily see that bending a fender. Inexperienced driver? First stall?



http://www.fordfuelinjection.com/?p=39

Explains it pretty well.
Click to expand...

well it stalled and i needed to get places fast so i ran to the hood opened it up smacked the IAC and got it unstuck and in my hurry to get back in truck i fell and smoked my head into the fender;brownbag;
 
mn_smokeater said:
well it stalled and i needed to get places fast so i ran to the hood opened it up smacked the IAC and got it unstuck and in my hurry to get back in truck i fell and smoked my head into the fender;brownbag;
Click to expand...

Is it bad if I chuckled a little at this? :icon_rofl: :haha:
 
Ford used to call the the Air By Pass Valve - Idle Speed Control.

It does exactly what it sounds like. It controls the idle and allows air to bypass the throttle blade. It used during start-up, idle, and deceleration to prevent stalling.
 
ok next question: as a rule, does the iac only open to a set distance? or does it dynamically open to varying levels?
 
varying levels,the computer sends a varying voltage to maintain a given rpm...this is why when the engine is loaded some,such as letting the clutch out some without touching the throttle,the engine will thrttle up(as much as the iac will allow)to try to maintain rpm.
 
ok, as a rule is all air needed at idle provided from the iac, meaning the butterfly is 100% closed and the iac is what makes it idle?
 
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