Too much idle airflow

[benno25]

Hi,
I've recently put a Harrop Hurrican ITB intake manifold on my LS3 and find I am getting too much idle airflow. Has anyone else had a similar issue to this (not necessarily with an ITB intake) and how did you get around it?
The motor is basically a stock LS3 with a 227/243 comp cam.
It will idle at around 900rpm, however this is with the IAC fully closed and around 0-5 degrees timing, so not ideal at all. This means the revs will hang a fair bit when coming to a stop unless I pull a heap of timing from the main timing table also. Not sure how I'm going to get around this issue.

Cheers
Benno

[mecanicman]

Never worked on or seen a harrop intake. Have done itb intakes. Had to go old school, talked to a guy that did old 8 stack alcohol fuel injection. Need to get an airmeter like the one shown in link. Then use feeler gauges to check throttle blade openings, keep closing a little at a time keeping them all balanced with air meter gauge until you regain control with your iac.

http://www.hilborninjection.com/prod...=438&CatId=231

[SSUte01]

If you've reached the physical limitation of preventing air bypassing the IAC path and going around the blade, there isn't a whole lot you can do. I have done a dual 4150 setup (it was more for looks than airflow requirement) that I modified as best I could to allow the IACs (I only plumbed one as the second I blocked in a further attempt to restrict air) to control the idle air but the throttle blades were simply not well enough (or perhaps deliberately designed as such) machined to not let excess air through. I, like you, used timing and fuelling to control the idle speed and get the IAC working. I should mention this was in P/N, in gear with the additional load it was ok, still leaner than ideal and less advance than ideal. Only other step is to increase idle speed to say 1000 to get the IAC in range or try and figure out a way to close off the blades more effectively. Sorry I couldn't be of more help. As an aside, triple check you have no leaks anywhere, this hi-ram setup did, which wasn't helping either.

[benno25]

Thanks for your help.
I'm going to try disconnecting all the vacuum hoses going to and block them off on the intake. I may be able to identify if the extra air is coming from one of those lines, or whether I'm just at the physical limitation of limiting airflow. The lines going to it are the HVAC, brake booster and the PCV.
The intake is great otherwise. Really smoother out my cam, plus the throttle response is awesome!!
Cheers
Benno