Some operating explaination on the intake air control is in order because there is some missunderstandings and some additional info that needs to be known.
The throttle body has a stop to keep the plate from fully closing.
There are two reasons for this and why the stop is never an adjustment point to fix idle issues away from the factory setting.
1. It allows air by the plate as a min hot idle without the IAC being opened.
2. If allowed to fully close on a hot engine, the throtle body will shrink ID size and grab hold of the plate.
So it's set opening is needed as the base idle for the system.
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Next, the IAC is a spring loaded dashpot action that is pulsed by the PCM to mantain variable opening 'against' it's spring as a way to have very tight control over air bypassing and maintain idle to within +/- 50 rpm.
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Additionally, the IAC needs to open wider for cold starts and higher idle.
Needs to respond to additional engine loads such as A/C, lighting, power steering loads etc.
As well the IAC needs to be allowed to close down during decelleration but still maintain enough air to keep the engine from stalling.
Bottom line is anything done to alter the airflow dynamics can cause a change the IAC spring loaded dashpot may be subject to.
Also the mass air meter can be subject to the same dynamics it it's area and change metering output to the PCM..
The factory setup has been fully engineered to meet all the operating conditions.
Make changes and you can possibly alter the results.
Good luck.