Q: How to address a vacuum leak at the bottom of the throttle body?
A: The TBI unit is attached to the top of the intake manifold by several bolts. These fasteners can sometimes work loose from vibration and temperature changes during normal engine operation and cause a vacuum leak. If you suspect that a vacuum leak exists at the bottom of the throttle body, obtain a length of hose. Start the engine and place one end of the hose next to your ear as you probe around the base with the other end. You will hear a hissing sound if a leak exists, but be careful of hot or moving engine components. Remove the air cleaner assembly, tagging each hose to be disconnected with a piece of numbered tape to make reassembly easier. Locate the mounting bolts at the top of the throttle body. Decide what special tools or adapters will be necessary, if any, to tighten the fasteners. Tighten the bolts to the torque, but don't overtighten them, as the threads could strip. If, after the bolts are properly tightened, a vacuum leak still exists, the throttle body must be removed and a new gasket installed. After tightening the fasteners, reinstall the air cleaner and return all hoses to their original positions.
Q: How to replace components of the fuel meter body/injector assembly?
A: When replacing parts of the throttle body/injector assembly, first relieve fuel system pressure and disconnect the negative battery terminal. Remove the throttle body by disconnecting the electrical connector and fuel lines. Drain the cooling system, remove the air intake duct, resonator, and fuel meter body by detaching connectors, vacuum hoses, and the accelerator cable. To remove the upper intake manifold, take out the ignition coil/module assembly, EVAP purge valve, and then detach the manifold. Poppet nozzles are removed by squeezing tabs, and the fuel injector can be pushed out after removing its hold-down plate. The fuel pressure regulator is removed by taking off its clip. During installation, replace and lubricate O-ring seals, press the injector into the throttle body, install the hold-down plate, and snap poppet nozzles into place. Check for fuel leakage post-installation.