Sounds like the ECU is holding in it's cold start strategy. The comments here about coolant and the coolant sensor are what I was going to suggest, especially if your weather has suddenly turned cold - temp sensor may well have been exposed in the cooling system by a low coolant level which would fool the ECU. You will be burning excessive fuel while this goes on, so don't leave it too long to sort out. One other point of note is that if it keeps holding the engine at high revs while still relatively cold, you may be incurring engine wear. If it had been a carb car, there would also have been the issue of a rich mixture dumping petrol on the bores when cold and washing off the lubricant. Believe me, this is a good way to kill an engine in short order.

You should be able to use the Gunson's Home Diagnosis unit to work out what's up: even if it's not ODB-2, it may have the precursor system, or a proprietary Toyota diagnostic port on the ECU. What's wrong with running it into a Toyota dealer? It would take them only a few minutes to do the diagnostic and this should be relatively cheap.