I have a friend who has a gs300 also like mine. his is a 05 , he is driving car is perfectly fine no noise or anything out of no where car is still running and just not driving anymore. then he has to put it in park shut off car and turn it back on and its back to normal. it seems like the car goes into limp mode what can he check first. yes i said it correctly the car is in d4 and it just doesnt move anymore.

 

A vacuum leak can cause that type of situation. Open the hood check the vacuum lines and such. If everything is fine. Find out if it still happens and post up.