Deceleration Control (Decel)

Fig. 31 Checking For Vacuum At Vacuum Hose #6:

NOTE: If the dashpot diaphragm in the throttle controller is damaged or if vacuum to the dashpot is interrupted by leaks or blockages, the correct idle speed cannot be obtained. The idle speed will be excessively high when the engine reaches operating temperature.

1. Check the idle speed.
a. Warm up the engine to normal operating temperature (cooling fan should cycle on and off once).
b. Connect a tachometer to the engine.
c. Idle speed should be (in neutral, with A/C OFF):
800 +/- 50 rpm (Manual Transmission)
750 +/- 50 rpm (Automatic Transmission)
d. If the idle speed is excessively high, check the vacuum to the throttle controller.
2. Check vacuum to the throttle controller.
a. Disconnect the #6 vacuum hose from the throttle controller and check for vacuum, Fig. 31.
b. If there is no vacuum available, check #6 vacuum hose for leaks or blockages. Repair or replace as necessary.
c. If the vacuum hose is OK, connect a vacuum pump to the throttle controller and apply vacuum. If throttle controller fails to hold vacuum, replace it and re-test.

Fig. 32 Adjusting The Throttle Controller (M/T):

3. Check operation of the idle controller.
a. With the engine idling, disconnect #6 vacuum hose from the throttle controller.
b. The engine speed should rise to 1700 +/- 300 rpm.
c. If the engine speed is not within specification with the idle controller disconnected, adjust it with the adjustment screw, Fig. 32.
d. If the rpm does not change, check the throttle controller linkage for free movement or damage.
e. If the linkage is OK, replace the throttle controller and re-test.