Relieve the fuel system pressure, then disconnect the cable from the negative terminal of the battery and drain the cooling system. For the upper intake manifold, disconnect the IAT electrical connector, remove the air filter housing and air intake duct, disconnect the large ETC connector at the throttle body, and disconnect the Automatic Idle Speed motor, Throttle Position Sensor, and Manifold Absolute Pressure sensor connectors. Also, disconnect the vapor purge vacuum hose, Positive Crankcase Ventilation hose, and tag and disconnect the power brake booster and Leak Detection Pump or Natural Vacuum Leak Detection system vacuum hoses from the manifold. Remove the two bolts securing the EGR pipe to the intake manifold, then remove the EGR pipe. Next, remove the upper intake manifold bolts and separate the assembly from the lower intake manifold, ensuring to cover the intake manifold runners to prevent objects from falling in. For the lower intake manifold, disconnect the fuel hose fitting, remove the fuel line, remove the ignition coil pack and bracket, disconnect the heater supply hose and engine coolant temperature sensor, and remove the fuel rail and injector assembly. Disconnect the upper radiator hose, remove the bolts and lower intake manifold, and if stuck, carefully pry on a casting protrusion without damaging the gasket mating surface. If installing a new lower intake manifold, transfer all fittings and sensors. Remove the lower intake manifold gasket retaining fasteners and gasket, then clean the mating surfaces thoroughly. Use a tap to chase the threads in the bolt holes and apply a 1/4-inch bead of RTV sealant to the cylinder heads-to-engine block junctions. Install the lower intake gasket and tighten the retainer fasteners, then lower the lower intake manifold into place and install the mounting bolts finger-tight, followed by tightening them in three steps to the specified torque. For the upper intake manifold, check the condition of the rubber seals in each intake runner and replace any damaged seals. Install the upper intake manifold onto the lower intake manifold, clean the manifold bolts of old sealant, apply medium thread-locking compound, and install the special screws carefully. Tighten the mounting screws in the correct sequence to the specified torque, then reinstall the remaining components in reverse order, refill the cooling system, start the engine, and check for leaks and proper operation.