Dave,
i'm not getting at the rust/oxidisation issue with using sea water. Get your voltage up firstly to 14.1v. Your ignition timing will be dramatically off and it will run rich as the processor speed for the computer is running slower, hence your injector pulse widths are longer than they should be. The computer would recognise the low voltage anyway and turn on the engine check light. Do you have one hooked up?
Back to the water issue, the 1jz and all injected Toyota engines need a water temperature of between 86-90deg celcius. Old holdens run around 72deg celcius, it might have been fine for your 502ci engine but the water "could" be too cold for the engine to ever get out of warmup mode. This would decrease ignition timing and increase fuel injection dramatically and may be what you are seeing. How hot does she run?