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I'd start by duplicating the hole size from your factory throttle body, and enlarge from there as necessary until you get the desired iac counts where you want them.
I think 1/4" would be too much, btw. You can always go larger, can't make it smaller. lol. Maybe someone here that has a stock throttle body can check for you.
1/4 inch is way too much. There were/are old threads talking about drilling hole in throttle bodies, as it was common years ago in the aftermarket ones. Do a search.
Update, ended up with a 10/64th hole in the throttle body, and car idles great now. Thank you everyone for the help.
The only other thing I came across was a reference to some sort of sleeving for the BBK throttle body's idle circuit back in the day, but I can't seem to find what this entails. Does anyone happen to know what this mod was?
If I remember correctly, some aftermarket throttle bodies had cutouts in the casting from the IAC port to the plenum. Sleeving was a way to ensure the IAC air got into the idle manifold, and not the plenum. This is a stock throttle body from an early L98. See the cutouts? Some aftermarket throttle bodies duplicated this. Not good for an LT1. Glad everything is working now.
Absolutely do that. Or look into the sleeve mod. Your BBK is dumping IAC air into the plenum, And that does look like a 52mm. BTW the stock manifold opening is 52mm as well. I have a BBK 58mm, and it does not have those channels. Just like this.
Last edited by MaxLean; Mar 9, 2024 at 08:27 PM.
Reason: Added pic.
So! After everything, the issue did turn out to be a misstimed cam! It was off by a tooth as seen in the photo below.
And that was causing the running issues all along! Although, I still think drilling the hole was a good idea, as with it, my idle steps are 20-25 when warmed up.
