If we have an idle air control valve...then whats the point of the idle adjustment screw on my throttle body?

And at idle...the throttle blades shouldnt be completely closed right?

Im confused as to how the iac works....Does it suck in air through that valve at idle and then use the throttle body when the car starts moving? (thats why i ask if the throttle blades can be closed at idle)

..i feel retarded asking this

 

What would be "retarded" would be assuming without research, and that's why this place exists.

The throttle body should be adjusted to admit enough air so that the engine can maintain a 500-550 RPM idle at full operating temperature, in gear, with the IAC fully closed and disabled. That is the purpose of the throttle stop adjustment screw. This is called the "Minimum Air Position" of the throttle plates. This is also the point at which the TPS should be adjusted to the 0.54VDC output. The ECM program is designed to use this as a base position for proper operation. If, as a result of improper adjustment, the ECM has to add IAC steps to maintain target idle RPM, the number of available steps for stall prevention and idle RPM control would be reduced.

Once these adjustments are made, the IAC has the ability to admit enough extra air to control the target idle RPM, trim the extra air during normal operation to prevent stalling on decelleration, add idle RPM when the A/C compressor is running, and raise the idle RPM for fast warmup on cold engine starts. With a fully closed throttle, the IAC may not be able to admit enough air to perform all those functions, so some throttle plate opening is necessary.

Further, with a fully closed throttle at idle, all intake air would be through the IAC air passage. The air on either side of the throttle plates would be completely stagtnant. This presents a problem when the throttle is opened, since all that air has to get moving from a completely static state to a flowing state, contributing to hesitation on throttle tip-in. Having some air flowing past the throttle plates at all times establishes some air flow so that hesitation is minimized.

The correct adjustment also makes for a more reliable system, since in the event of failure of the IAC, the engine would still have a chance to idle, albeit at a lower RPM, rahter than completely die. This redundancy is similar to the secondary path for fuel pump power, or backup resistor packs in the MEMCAL, or splitting the primary power through several fuse links instead of just one. It's simply good engineering and design.

 

thank you very much, that was alot of help.

 

Man VADER, I think that could have not been explained any better by a GM manual.....lol. GREAT JOB, THANKS...