Stall Problems On Gs 300 Sport Sat Nav

[west highlander]

I've recently aquired GS 300 Sport, my wife was out driving and without any warning the car lost power steering, the engine stalled and the dash and sat nav went blank. With difficulty my wife managed to control the car, however being disabled, no power steering put her life at serious risk of injury or worse. After removing the key that was difficult to do the steering wheel never moved. After starting the car again everything came back to life and was fine. Four days later the problem re-occurred, whilst I was driving, loss of power steering, engine stalled. This time removal of key was easy, no loss of dash or sat nav. I have noticed also that the rev counter has been irratic, low tick over 500 rpm down to virtual stall when slowing to a halt or turning corners. Has anyone suffered this problem, ideas would be extremely welcome before going to garage.