Originally Posted by 64nailhead
Not sure how the Holley TBI works, but based on you say it idles properly when cold and then poorly when warm, I'd check vacuum at cold idle and then hot idle and see what the difference is. Does the Holley system work on maf or map sensor.
After rereading your post, do you have a complete Holley EFI system or a Holley replacement throttle body using the GM ECM. If the latter, then I would definitely guess that you have an intake leak, a bad IAC.
That's my guess. Some more info would be helpful.
Regarding the head gasket, are you using coolant? Are you getting excessive pressure in the cooling system? Anything smelling funny out of the exhaust? Smoking white? Any sludgy residue on the dipstick or oil fill cap? If no to all of those, I would say your headgaskets are fine.
The Holley TBI is just a bolt on replacement, same as the stock, just a larger cfm. I haven't checked the vacuum yet, I've been meaning to do that for quite some time now, ill see about checking it after work though. And it is a stock MAP system. I'm using green coolant in the system, and I can't seem to keep it full I'll check that again after work. And no I don't see anything mixing in my oil, or dipstick. I'll have to pull the valve cover to see any farther with my set up. As far as exhaust goes it's hard to tell because it's been cold out lately, and I get the usual white exhaust in the morning. Although now that I think about it, it does take awhile for that white exhaust to come, I don't get it as soon as I strat up