The car dies within 5 minutes of starting. Idle will get progressively worse until it won't idle at all and you have to give it gas to keep it going - keeps getting worse until not possible to keep the engine running at all. Re-starting requires "flood start" - foot to the floor and crank like crazy - in about 30 seconds of cranking it may start, acting exactly like a badly flooded engine, cylinders slowly kicking in until it finally runs.

This problem was coincident with a leaking head gasket, and I have wondered whether coolant might have messed up the O2 sensor(s)... But I wouldn't think that a bad O2 sensor would be able to throw the mixture off so far that it would die...

What I have done:

Replaced crank sensor - no change.

Checked fuel pressure - ~45psi, and does not drop as the engine dies.

Removed exhaust to check for plugged cat - dies exactly the same (except much more loudly).

This vehicle has the "partial" OBDII (not fully implemented until 1996 as I understand...?) - does not show any codes.