Here is the iac on a 2005 trailblazer? - 2005 Chevrolet TrailBlazer

2005 Chevy Trailblazer service manual said the same 345-395 kPa (50-57 psi)

IAC - idle air control motor , Vacuum leaks . Dirty throttle body . Videos on youtube for cleaning throttle body , IAC , and finding vacuum leaks .
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Sounds like a vacuum leak or iac , check engine codes.

have your IAC and mass air flow sensor checked surging can be a problem in either one IAC( intake air control) or idle air control.
does the car have any obd2 codes? have it scanned for codes

Here see if this helps

need to clean or replace idle air control motor (iac)

Doesn't have one. We have an Electronic Throttle Control or ECT. The idle air control is controlled by your PCM and throttle body, so there isn't a valve. What's the problem or what problems are you experiencing? Chances are it's a dirty throttle body.

This sounds like an IAC problem.at idle the iac controls the air flow through the throttle body.try a good throttle body cleaning and dont forget to clean the iac too.

need to get codes to repair, have seen alot of these vehicles go thru the throttle position sensor which is the complete throttle pedal assembly

A bad IAC unit will cause poor driveablility and poor/high idle, and also stalling and starting issues. There is really no harm by being bad but during rapid deceleration if the IAC does not catch the RPM's the engine could stall out; not a good thing if you were going 60 mph. Remove the IAC motor and clean the valve and also the chamber that it goes into with a good throttle body cleaner and that should really help. Carbon buildup is a big factor in IAC failure. Most CEL will not show a malfunction code with a bad IAC motor.