To replace the upper intake manifold, start by disconnecting the cable from the negative terminal of the battery, ensuring to relieve fuel system pressure if the lower intake manifold will also be removed. If the engine remains in the vehicle, disconnect all hoses and wiring from the throttle body, pinching off coolant hoses to prevent draining the cooling system, and label them for clarity. Next, disconnect the air intake tube from the throttle body, remove the throttle body bracket and upper intake manifold brace, and disconnect all wiring and hoses from the manifold. Remove the two intake manifold mounting nuts and four bolts to take off the upper intake manifold, checking the gasket for damage; if it is in good condition, it can be reused. For the lower intake manifold, first remove the upper intake manifold, then if replacing the lower manifold, remove the fuel rail. If only replacing gaskets, disconnect the fuel supply and return lines without removing the fuel rail. Remove the interfering brace and the ten lower intake manifold bolts to detach the lower intake manifold. Discard the old gaskets and clean the mating surfaces thoroughly before installation, which should be done in reverse order using new gaskets and tightening the bolts in a criss-cross pattern from the center outward.