Models Produced Up to March 1990

Before making any adjustments to the idle speed or air/fuel ratio, observe the following conditions.

^ Perform vehicle self diagnostics, make any necessary repairs (there must be no fault codes stored in memory when adjusting idle speed or air/fuel ratio).
^ Engine is at normal operating temperature.
^ All electrical loads turned OFF (A/C, cooling fan, heater blower, etc.)
^ Crankcase ventilation hose disconnected and plugged on manifold side.

1. Disconnect and plug vacuum hose from carbon canister shut-off valve.

2. Remove cap from CO tap tube and connect emission analyzer.

3. Start engine and idle.

^ Idle speed must be 770-830 rpm (800 rpm preferred).
^ CO content must be 0.3-1.2% by volume (0.5-1.0% preferred).

If OK, no adjustment necessary.

If not OK, continue.

Diagnostic Connectors - Activating Self Diagnostics:

4. With engine idling below 2,000 rpm, connect jumper wire between diagnostic connectors (as shown in diagram) and leave connected. It is not necessary to connect LED test light for this procedure.

With the engine idling and jumper wire installed, the ECU will:

^ Fix ignition timing at 12~ advance.
^ Fix idle stabilizer valve signal at a constant value.
^ Switch to "open loop" operation (no oxygen sensor feedback control).
^ Reset learned value for idle stabilizer valve signal to zero.
^ Assume an engine coolant temperature of 176~F (80~C) regardless of the actual temperature (this is why it is important that the engine is fully warmed up).

Idle Speed Adjustment Screw Location (arrow):

5. Turn idle adjustment screw until idle speed is within specified range.

If idle speed is too fast and will not adjust down, check idle stablizer valve. Testing and Inspection.

If idle speed is adjusted to within specified range, check CO.

^ CO content must be 0.3-1.2% by volume (0.5-1.0% preferred).

If OK, no further adjustment necessary.

If not OK, continue.

5. Turn engine OFF and remove CO adjustment screw anti-tampering cap.

CO Adjustment Screw Anti-Tampering Cap Location (arrow):

a. Lightly center punch cap and drill small hole in cap.
b. Screw a sheet metal screw into drilled hole.
c. Remove cap by pulling on screw with pliers.

NOTE: It may be necessary to remove the air mass sensor to gain clear access for removing anti-tampering cap.

6. Start engine and let idle.

7. Turn CO adjustment screw until CO content is within preferred specification range.

^ Clockwise - CO content increases.
^ Counter clockwise - CO content decreases.

8. Re-check idle speed and adjust if necessary.

9. After idle speed and CO content are adjusted to within specification, remove jumper wire from diagnostic connectors, rev engine over 2,000 rpm several times then let idle and re-check idle speed and CO content.

If idle speed and CO content are not within specified range after reving engine, repeat adjustment procedure.

If idle speed and CO content are OK, disconnect exhaust analyzer, install CO tap tube cap and new anti-tampering cap.