After replacing a cracked intake manifold on a V8 97 Tbird that overheated and stalled the car fails to idle. The engine runs and sounds ok as long as you stay on the throttle, as soon as you let off it stalls. As soon as you start it coolant overflows the degas bottle. We tested and had approx 120 psi on each cylinder. We cranked the engine with only one spark plug in at a time but the coolant level was stable. We then tried adjacent cylinders and with plugs in 3 & 4 the coolant surged out of the degas bottle. We assumed this meant the head gasket was blown between 3 & 4. But with the head removed, the gasket, head and cylinder wall all look fine. Any suggestions?