Idle Speed and CO Adjustment

1. Initial setup:
a. Remove the plug from the timing window at the top of the bellhousing (on manual transmission equipped vehicles).
b. Disconnect and plug the crankcase vent hose from the valve cover.
c. Ensure the exhaust system is sound.
d. Ensure that there are no engine vacuum leaks.
e. With the engine at normal operating temperature, (allow the engine fan to cycle at least once).
f. Briefly accelerate the engine to above 3000 RPM at least three times to warm up the oxygen sensor.
g. Turn off all electrical loads (lights, radio, A/C, etc.).
Note; When taking readings or making adjustments, ensure the engine fan is not operating.
2. With the engine at idle, check the ignition timing. Timing should be 6° +/- 2°.
3. If the ignition timing is not within specs, adjust by loosening the hold down clamp and turning the distributor.
4. Check the idle stabilizer valve. It should be making a slight humming noise. To make sure the valve is operating, disconnect then reconnect the harness plug. The idle speed should change noticeably.
5. Check the idle valve switch by disconnecting and reconnecting the plug on the switch. The idle speed should change noticeably.
6. Connect an exhaust gas analyzer to the vehicle by removing the CO sampling cap from the exhaust pipe and connecting the analyzer adapter to the fitting.
7. Check the oxygen sensor for proper operation by removing the oil filler cap while watching the CO meter. The meter should vary slightly, then return to it's original position.
8. Shut off the engine and connect a tachometer, and disconnect the oxygen sensor.

Note:
It is critical that the ignition be switched OFF before disconnecting the oxygen sensor to cancel the memory in the ECU. Failure to do this will result in an incorrect mixture and idle speed setting upon restart.

9. Restart the engine and momentarily accelerate the engine above 2100 RPM at least four times to cancel the control units hot start fast idle function.
10. The idle speed should read between 925 and 1025 RPM. If it does not, turn the idle air bypass screw on the throttle housing until the idle speed falls within this range.

Fig. 9 CO Checking Specifications:

11. Check the CO reading at idle. The reading should match the values shown in Fig. 9.
12. If the readings are not within the specifications shown, remove the adjustment screw plug in the air flow meter by first drilling a 2.5 mm (3/32 in.) hole in the center of it, then installing a screw in the hole and removing the plug with pliers.

Fig. 10 CO Adjustment Specifications:

13. Using a 5mm allen wrench, turn the adjusting screw until the CO value matches the values shown in Fig. 10.
14. Reconnect the oxygen sensor and check the idle speed, readjusting if necessary. Continue adjusting the idle speed and CO content until both are within specifications.
15. Reconnect the crankcase vent hose to the emission control valve. Shut off the engine and remove all test equipment.
Note; If the CO% increases significantly when the crankcase ventilation hose is reconnected, The cause is probably not incorrect adjustment. It is probably due to the engine oil being contaminated with fuel as the result of short distance driving. Changing the oil is a short term solution.