Throttle Body: Testing and Inspection

To determine if the internal passages of the throttle body are clear and functioning properly, perform the checks listed below.
These checks are to be performed with the engine coolant temperature at 176 - 205°F (80 - 95°C).

EGR VALVE, CONTROL VACUUM CHECK:

EGR Vacuum Port Location:

1. Disconnect the vacuum hose from the throttle body EGR vacuum fitting and connect a hand vacuum pump to the fitting.

EGR Port Vacuum Curve:

2. Start the engine and check to see that, after increasing the engine speed, vacuum raises proportionate to engine speed.

PURGE CONTROL PORT VACUUM CHECK:

Purge Hose Vacuum Source:

1. Disconnect the vacuum hose from the throttle body purge hose fitting and connect a hand vacuum pump to the fitting.

Purge Port Vacuum Curve:

2. Start the engine and check to see that, after increasing the engine speed, vacuum remains fairly constant.

NOTE: If there is a problem with the changes in vacuum in either test, it is probable that the throttle body requires cleaning. Refer to COMPONENT REPLACEMENT AND REPAIR PROCEDURES

For diagnosis and testing of the motor position sensor (MPS), idle switch, throttle position sensor (TPS) and the idle speed control (ISC) servo, refer to COMPUTERIZED ENGINE CONTROLS.