Emission Control Systems: Adjustments

1. Warm engine and make sure that idling speed is to specifications.

2. Disconnect vacuum hose from throttle positioner.


NOTE: On 1979-80 20R and 1981 22R engines, connect the disconnected hose directly to vacuum connection on intake manifold. On 1981-82 4K-C engines, plug the disconnected hose. On 1981 3A-C engine, disconnect and plug both hoses from throttle positioner diaphragms. On 1982 3A-C engine, disconnect and plug hose from diaphragm B only.

3. Race engine and then release accelerator pedal. The engine speed should be as specified in the following chart:

Engine RPM

3K-C 1500
1974 2T-C & 18R-C 1400
1975 2T-C w/Man. Trans 1500
1975 2T-C w/Auto. Trans 1400
1974-76 4M w/Man. Trans 1300
1974-76 4M w/Auto. Trans 1200
1975-77 20R w/Man. Trans 1400
1975-77 20R w/Auto. Trans 1200
1977 2T-C w/Man. Trans 1400
1977 2T-C w/Auto. Trans 1200
1978 20R 1050
1978 4M 950
1978-79 2T-C w/Man. Trans 1400
1978-79 2T-C w/Auto. Trans 1200
1979-80 20R 1050
1980 3T-C Fed. w/Man. Trans 1600
1980 3T-C Fed. w/Auto. Trans 1300
1980 3T-C Calif 1400
1981 22R 1050
1981.82 3A-C 1400
1981.82 3T-C 1400
1981-82 4K-C 2000


4. If speed is not within specifications, adjust by turning throttle positioner screw.

5. On 1978 4M engine and 1980-82 3T-C engine, reconnect hose to throttle positioner. The engine should return to idle within 10 seconds on 4M engine, or within 1-3 seconds on 3T-C engine. If not, replace vacuum transmitting valve.

6. On 1981-82 4K-C engine, check restrictor jet by reconnecting hose to throttle positioner. Check that engine returns to idle speed within 1-6 seconds.

7. On 1981-82 3A-C engine, check vacuum transmitting valve No. 2 by reconnecting vacuum hose to diaphragm B and checking that engine returns to idle within 2-6 seconds.

8. On 1981-82 3A-C engine, check vacuum transmitting valve No. 1 as follows:

a. On 1981 vehicles, reconnect vacuum hose to diaphragm A.

b. Disconnect vacuum hose between thermostatic vacuum switching valve (TVSV) and vacuum transmitting valve (VTV) 1 at the VTV 1 side and plug hose end.

c. Disconnect vacuum hose from diaphragm B and plug hose end.

d. Accelerate engine to 4500 RPM and plug VTV 1 pipe. Make sure that stopper lever is separated from throttle positioner adjusting screw before lugging pipe.

e. Release accelerator and check that engine speed drops to 2500-3000 RPM.

f. Remove plug from VTV 1 and check that engine returns to throttle positioner setting speed within 3-10 seconds on 1981 vehicles, or 4-10 seconds on 1982 vehicles.

g. If system does not operate properly, check components individually.