New guy.... Hanging idle problems.

[Vandyket/a]

I'm new to hptuners so I had my 408 professionally tuned. Well since I got the car back I'm getting intermittent hanging idle. Sitting still the car idles fine but a lot of the time the car will shoot to 1600 rpm and hang until the car stops. It seems to do it less when the engines cold. Once the car stops within 2 seconds idle drops straight to normal. It's speed density tuned. Tps is reading 0-100 correctly even when the idle hangs I've cleaned the iac. What in the tune is most likely causing this.

[mecanicman]

Paste the below into a google search box. You will find your answers.

site:hptuners.com hanging idle

[Vandyket/a]

I googled it and seen a few different possibilities but even when the car idles at a stop the iac is at zero. I'm pretty confident I must have a vacuum leak from the iac going closed.

[blownbluez06]

You may have a vacuum leak, but if the idle ever comes down to a reasonable level, that is usually caused by too much cracker flow. Pressure check your intake and if you don't have a vacuum leak, log your cracker flow and reduce it and/or your rolling idle airflow as needed.