To take out the upper intake manifold, first loosen the cable connected to the negative battery, then take out the air filter assembly and the air intake duct. The second step is to remove the engine cover (where applicable), remove the connector on the electronic throttle body as well as any coolant hoses or other connector. In case of 3.0L engines, remove the electrical connector of MAP sensor, EGR electrical connector and EGR pipe. Also, disconnect EVAP hose, brake booster vacuum hose and PCV hose and in case of 3.7L engines, disconnect heated PCV valve connector. Label electrical connector and mark vacuum lines to reconnect, and dislodge the wire harness bracket nuts, and place the wiring harness out of the way. On 3.7L-powered engines, remove the throttle body end manifold brace. Unscrew the mounting bolt of the upper manifold brace(s) and loosen the upper intake manifold bolts, in the reverse order. Take out and dispose the intake-to-lower intake manifold gaskets. To install, ensure that the mating surfaces are not warped in case the gasket was leaking and use new gasket and ensure surfaces are clean and flat without any sealant. Fit the upper manifold to the lower manifold and attach the fasteners and tighten them in three or four steps to a measured torque. Install all the other parts in the reverse order reconnecting the battery and letting the Powertrain Control Module relearn the idle and fuel trim strategy. Once the engine is fully warm, then test the leaks of fuel and vacuum and have a road test. In the case of the lower intake manifold, the engine should be entirely cooled down before starting. Reduce the pressure in the fuel system and remove the negative battery terminal. In case of 3.7L V6 engines, empty the cooling system, and remove the upper intake manifold. Disconnect the fuel line between the fuel rail and the fuel injection electrical connectors between the fuel injectors and push aside the injector wiring harness. In 3.7L engines, loosen the 4 bolts that fix the thermostat case to the lower intake manifold and leave the coolant hoses fixed. Looseen the lower manifold bolts one after another reversing the order of tightening, until they are all loose, and then loosen the upper manifold bolts following the same procedure. Remove the lower intake manifolds(s) of the engine and remove the manifold gaskets, taking care not to rub all the gasket material off the mating surfaces. Install lower intake manifold gaskets on the cylinder heads, install the lower manifold(s) making sure that the gaskets do not touch, and attach the fuel rail and injectors to the manifolds (on 3.0L V6 engines). Install and tighten lower manifold bolts step by step to desired torque and continue installation procedure in the reverse order, making sure that all the fasteners are solenched to the desired torque. In the case of 3.7L V6 engines replace the engine oil and filter followed by refilling and bleeding the cooling system.