I have a 94 lexus gs300 i start it in the morning and let it warm up for 10 minutes. as soon as i put it on reverse the car shuts off. i restart it again and begin driving, as soon as i come to a stop the starts shakings and shuts off. About a month ago it will do that and after 10minutes of driving no shut off when i stop, but lately its has been acting like its losing power and continues to shake after it warms up please help