4.3 - Throttle Body Removal and Cleaning ( ,  )

Periods of cold running, perhaps caused by a sticking thermostat, will cause the throttle body to become gummed up internally, potentially causing the throttle to stick partially open and also affecting Idle Speed Control Valve (ISCV) operation. It can also be the cause of an uneven or lumpy idle.

On the XJR, the throttle body is located under the inlet manifold so this must be removed first following the instructions above. Those with a ramps or a hoist may be able to gain sufficient access from underneath.

Release the throttle cable by carefully using a pair of long noses pliers to push off the retaining clip. Also disconnect the vacuum hose from the cruise control actuator.

Unbolt the heated part of the manifold, releasing the coolant pipes as necessary, and then unbolt the throttle body itself. The ISCV can be identified as a small nozzle in a drilling in the side of the main orifice, which controls the amount of air bypassing the main throttle butterfly.

On the bench, use carburettor cleaner or a similar solvent to clean out the body, butterfly and ISCV. Allow the cleaner to get into the ISCV drillings, but hold the body so as to avoid running down into the Throttle Position Sensor, which is contained in the plastic housing at the end of the throttle butterfly shaft.

Reassembly is simple. Make sure the cruise control actuator arm can fully actuate and release the throttle butterfly. No gaskets are used, so to avoid vacuum leaks, ensure the mating surfaces are smooth and clean. Bolt everything up and reattach the throttle cable, retaining clip and cruise control vacuum hose.