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For those who are still on stock ECU and have a wideband, you can adjust your A/F's at idle.
After everything is set up properly (vacuum, timing, idle), you ground the test connector and use the screw on the air flow meter (the one hidden under the aluminum plug) to adjust idle A/F's, this will affect RPM at Idle which should then be returned using the Idle adjustment screw on the TB. then check the timing (all with the test connector grounded).
As far as Idle A/F's (on all my engines and different set ups, with different wide-bands and only two constants, all had new Bosh o2 narrow band sensors replacing the factory ones and 90+ GT injectors instead of the 88-89 gt...)
I idle at 3 lights on the digital dash (4 lights is roughly 750 RPM) maybe 600 rpm with the engine at normal temp I get steady 14.9 A/F's. with the head lights off (under drive pulley, no PS/AC belt and a lightened or lightweight flywheel) the RPM's increase to 4 lights (close to or at 750 rpm) and the A/F's will be between 15.0 and 15.1 A/F's depending on outside air temp.
rpm at idle affects A/F's.
Under cruise I see 15.7-15.4 a/f's, very gentle on the throttle, any more throttle and I see 14.9-14.2, still in vacuum (all this under 3000 rpm).
Remember our primitive factory OBD1 set-up, loops the O2 reading after 3000 rpm so crossing that rpm with the same throttle will drop into the 12.9+- A/F's feathering the throttle above 3000 rpm can sometimes result in normal cruising A/F's (14.9-15.7).
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