Right, did some more on the car today.

Did a compression test and got readings of (1) 168, (2) 168, (3) 159 & (4) 165. That would suggest to me that the head gasket is OK?

Tried playing with some sensors:

ECT disconnected makes it run worse;
IAT disconnected makes it run worse;
TPS disconnected doesn't seem to make much difference;
MAP disconnected doesn't seem to make much difference;
TPS & MAP disconnected makes it stall;
ISCV disconnected makes it stall.

Substitued the coil pack, MAP sensor and EDIS for alternative units - made no difference.

All of that seems to be correct to me, so I'm no nearer a solution. And it's still throwing out water from the exhuast, but the compression test suggests that everything is OK...so I lost!!

HELP!