The IAC sucks air through its Idle Air Control Passage Inlet slot (see below) only at idle RPMs. Therefore, it can only suck in the Throttle Body cleaner at idle RPMs. What you want to do is to get cleaner into the IAC while the engine is running so the more you can keep it at ldle, the more cleaner you can get to the IAC. The engine will die when enough cleaner gets into the IAC to block off air flow but that's ok, the more that gets in there the more it can "cook" and loosen the crud that forms inside where the IAC is controlling the air flow.
It's actually easier to just remove the IAC and clean its plunger and the hole in the throttle body the plunger fits into, it is only held onto the throttle body with two small torx screws, T-25 I think.
That plunger is solenoid controlled so it moves in/out under the computer's control to control how much air it lets into the engine at idle RPMs. Cleaning its plunger and the hole in the throttle body it fits into will typically restore it back to 100% operation.
Finally, the engine gets its air via the throttle body via either the big round butterfly valve that opens when you step on the gas, or from the Idle Air Control Passage Inlet slot just above the butterfly valve. When the butterfly valve is closed, as it is at idle RPMs, then it must get air via the IAC... which if it's dirty, the engine won't run or won't run well at idle RPMs. Hope that helps.