Q: What are the steps involved in removing and installing the upper and lower intake manifolds on Nissan Maxima?
A: To begin the process of removing the upper intake manifold (plenum), disconnect the cable from the negative terminal of the battery and remove the air intake duct. Next, disconnect the accelerator cable, cruise control cable (if equipped), hoses, and electrical connectors from the throttle body, being prepared for some coolant spillage and plugging the hoses immediately to prevent excessive loss. Detach the spark plug wires from the spark plugs and remove them from the retainers on the plenum, then remove the distributor cap and set it aside along with the spark plug wires. Label and disconnect the hoses and electrical connectors attached to the plenum, remove the ground strap, and loosen the upper intake manifold bolts in reverse order of the tightening sequence before removing the upper plenum with the throttle body attached. For installation, clean the mounting surfaces of the intake manifold and upper plenum with lacquer thinner, ensuring all old gasket material or sealant is removed. Install a new gasket over the intake manifold studs, position the upper plenum onto the intake manifold, and tighten the bolts in the proper sequence to the specified torque, completing the installation in reverse order of removal while checking and adding coolant as necessary. For the lower intake manifold, relieve the fuel pressure and disconnect the cable from the negative terminal of the battery, then remove the upper intake manifold. Drain the cooling system, disconnect the electrical connectors from the coolant temperature switch and sensor, and remove the radiator hose from the thermostat housing. Label and detach any vacuum hoses that may interfere with the removal of the lower intake manifold, then remove the fuel rail and injectors. Disconnect the coolant pipes at the transmission end of the intake manifold, loosen the manifold mounting bolts/nuts in 1/4-turn increments until they can be removed by hand in reverse order of the tightening sequence. If the manifold is stuck to the cylinder heads, use caution to avoid damaging the gasket sealing surfaces while breaking the gasket seal. Carefully scrape away all traces of old gasket material and sealant from the manifold and cylinder heads, then clean the mating surfaces. Inspect the coolant pipes below the intake before installing new gaskets and the lower intake manifold, ensuring proper alignment over the dowels in the cylinder heads before installing the nuts. Following the recommended tightening sequence, tighten the nuts/bolts in three equal steps to the specified torque, and complete the installation in reverse order of removal. Refill the cooling system and change the engine oil, then run the engine to check for fuel, vacuum, and coolant leaks.