does this shutter happen only in park or while driving also? i doubt the iac is bad if its rock solid on idle speed and not jumpin, or sound like u have a cam lope. a bad MAP sensor can cause rough idle or stumble, along with the crank sensor also. this is why i asked if it did it all the time or not.

 

It happens at idle. In park or neutral or in drive at a stop light. I cannot tell it it doing it while driving. Seems smooth otherwise.