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Old 07-10-2013, 07:05 PM   #1
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SPI intake assembly

The intake manifold assembly as most of you know is composed of two parts, the intake manifiold and the split-port injection part. I cannot remember it's proper name right now...sorry about that.

On the second part there is a screw that looks to be used to adjust some setting. Can some one enlighten me as to what it sets in the scheme of things?

Is it an idle setting, some sort of mixture adjustment?

I ask since I just replaced the cylinder head, cleaned out everything, and now I find the car is not quite right at idle. I didn't adjust the screw, actually it's bent pretty badly so I couldn't adjust it if I wanted too. I don't think this is related to my problem but I'd still like to know what it is for.


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Old 07-10-2013, 10:48 PM   #2
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Originally Posted by p58ff View Post
I cannot remember it's proper name right now...sorry about that.
Throttle body.

Originally Posted by p58ff View Post
Is it an idle setting, some sort of mixture adjustment?
Neither. It is simply a non-adjustable mechanical stop for the throttle plate movement. It does not control idle speed directly. Your car is fuel injected, not carbureted, so old school idle speed screws, idle speed jets and float bowl levels don't apply. If you do manage to move it (usually after removing a factory installed anti-tanper device), the PCM will simply compensate for any small changes you've made.

The PCM controls the idle speed via the Idle Air Control Valve (IACV) using various engine sensors. Think of the IACV as a variable sized bypass hole or small passageway around the closed throttle plate. Modern engines use an IACV because idle speed is more accurately controlled by the PCM under a wide range of operating condition than it would be by an old style "fixed" - albeit manually adjustable - idle screw.

The Ford, or any modern system, relies on the throttle body and intake system being "air tight" for the system to work correctly - only air that passes the MAF (Mass Air Flow) sensor is used (metered air) for idle speed calculations by the PCM. Therefore, if you've had the thing to pieces and your idle is not inconsistent and low, you likely have a vacuum leak due to a loose fastener, loose clamp or perhaps a leaking or perished gasket somewhere after the MAF.
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