Do you have any way of checking your fuel pressure?

 

The best advice I can give, is check out http://www.chevythunder.com
Lot of good info and flow chart diagnosis. I'm in the middle of a similar problem I think I have traced back to faulty fuel delivery.

 

It almost sounds like the car could be getting too much gas. Like Mike said, I would check the fuel pressure if you can. It could possibly be the fuel pressure regulator is allowing too much gas to flow in and it's flooding. As soon as you take your foot off the gas, it burns the fuel and goes back to normal idling.

 

hey im new here and i was readin about ur problem an i had the same problem mine lead to in the tank the fuel pump neck had a crack in it so check all ur fuel lines and a would check the pump its self but i bet ur not gettin good presure

 

I realize this is an older topic but for anyone searching later, I recently had a very similar issue and traced the problem back to the "Vacuum Adjustable Fuel Pressure Regulator", I was able to get a Vacuum Delay Valve from NAPA that fixed the issue.

Sadly there are many causes for this type of problem, figured I'd add another possibility.