Just a quick thanks to Fred (Injuneer) for your help. I finally got a chance to go back and work on it again and the IAC was the culprit. Changed out the IAC and I finally got my idle down to a proper range around 700 RPM. On to other issues now.

 

This does, though...



OP, are we sure this is a real, complete LT4? The reason I ask is if you were to put an LT4 intake on LT1 heads, they might not completely seal at the runners, because of interference. That could create a vacuum leak and the high idle.

What are your IAC counts when scanned?

You can check the TPS with just the key ON and engine not running. Watch your scanner as you slowly go from no throttle and press the pedal to full throttle. It should ramp up smoothly.

 

This LT4 is the real deal. It was a complete motor out of a 96 Corvette Grand Sport. There aare no issues with intake and heads fitting properly. Right now, I have the LT4 motor running on a stock SS LT1 ECU. And I haven't found anyone locally who can tune it. I bought an LT4 ECU but my car has an automatic transmission and no LT4 Corvettes came with automatics. So I wonder what problems that will cause.

BTW, shoebox, thanks for your help on supplying much needed technical information on your sight. It was very helpful.

I am not well versed in OBD II diagnostic tools and the guy here who knows what to do is too busy right now to lend a hand. But I did find that I had a PS high reading pop up and a TPS reading too low, as well.