holley idle issues

I had a similar problem that drove me nuts for over a year. Turns out there was a little notch worn in the throttle cable that would just hold the throttle open enough to cause the engine to idle at 1000-1200 rpm. Would happen when cold and wouldn't happen when I was out there fiddling with it.

When I noticed the worn area in the throttle I was able to temporarily fix it by putting more slack in the cable adjustment until I got a new cable.

My not be your issue but certainly worth checking.