2000 Jaguar S type 3.0

My car turns off at stop signs and red lights. When the vehicle is running at over 30 miles it seems to run ok though. The car is very shaky as it comes to a stop and it usually turns off when I come to a stop. I usually just put it in neutral and rev the engine. My car has had this problem for months now and although I had the upper and lower intake gasket replaced it is still doing the same thing. The two fault codes are P0171 and P0174. Thank you for your help!