Ok, I missread, you still have the 2 bbl on the car, just a 4bbl intake manifold?If you have fire coming into the intake then you may have a valve problem. Did you change the intake yourself? Double check your spark plug wiring, I had a Camero once that had a similar set of symptoms and it ended up being a swithced set of wires. Garage I took it too didn't find the problem, I eventually discovered the error myself.