Thanks for that, that is interesting what constitutes a reset of the ECU? For instance if the battery to totally flat for a long period of time or has been briefly disconnected can this cause a reset of the ECU? This did occur recently and since then only around 10 miles has been covered? Could the ECU still be 'learning' again?
Just as an additional point the engine is no longer in a Lexus and it is not mated to its original auto box, but on a conversion to a Supra 5 speed manual box, but I guess the ECU will still make the adjustments to the idle speed?
Thanks for your responses.