1974 Models
- Disconnect vacuum hose between mixture control valve and vacuum switching valve (at vacuum switching valve). Start engine, place hand over mixture control valve inlet port, and check for vacuum.
Courtesy of © TOYOTA, LICENSE AGREEMENT TMS1002
- If vacuum is felt, mixture control valve is defective. Apply vacuum to disconnected vacuum hose, air should momentarily flow through mixture control valve. See Figure.
- With vacuum hose still disconnected, connect a vacuum gauge to vacuum switching valve and position gauge so it may be seen while driving vehicle. Road test vehicle.
- Increase vehicle speed to at least 45 MPH. At 39-43 MPH, vacuum should be indicated on vacuum gauge. Slowly allow vehicle to decelerate. At 26-36 MPH, vacuum gauge reading should drop to zero (0).