Not looking to start an argument, but IMPO these things are very rarely an air leak or bearing problem.. Fuel tank, maybe.. But very unlikely with a new one.. I think it just needs more messing with. Maybe try a hotter(or just another fresh) plug as suggested. But as you said, if you can get the low and high good, then just live with blipping it as necessary.. But then I am used to that with most of my big block engines.. A Nova I would expect to idle more nicely though. (my LRP ZR.30X idles perfectly though..) Basically, just keep at it...