i replaced a head gasket and intake manifold gasket my car ran perfect before i took it apart except it over heated. and i had oil in the coolant. i got it all back together and started it it ran perfect for about 30-45 seconds then it died abruptly now the only way it will start is if i hold the gas pedal to the floor and it runs extremly bad wont run at an idle and only goes to 3.5 rpm at the highest and i gotta feather the gas to get it to that i changed plugs and wires any ides on what is happening?