Workshop Manual Section D:04:14 will lay everything out and give you the exact specs you should be seeing.

LAMBDA has 3 modes of operation for target duty cycles it applies to the Frequency Valve:
  • The first is Open Loop for when the O2 sensor is offline because it is not yet warmed up. 40-50° Steady Reading
  • The Second is for when Enrichment is triggered. This occurs when the LG, or Light Green wire is grounded. Both the WOT switch and the Thermal Switch in the Y-pipe are spliced into this same wire and can trigger this by WOT or coolant temp of 15°C/59°F or less. 50-60° Steady Reading
  • The third and final is normal operation. O2 Sensor is reporting back, and neither the WOT or Thermal Switch is triggered. 35-45° Pulsating


If you want to test the LAMBDA ECU, you can do it easily once it's warmed up. Ground the O2 lead and it'll hit 87° minimum. Apply 1.5V and it'll hit 20° maximum. That'll let you know if it's bad or not. Just in case too, disconnect the WOT Switch, and then check the LG wire to see if it's grounded. That'll tell you if the Thermal Switch is bad and screwing with things by constantly running too rich when not needed. Of corse, check all grounds as well. For the hell of it, also gently snug up the 3 brass screws to ensure there are no leaks. Probably not related, but it's good to ensure you're not running unbalanced cylinder banks.


Quote Originally Posted by David T View Post
I have found that the cars with the "hotter" cams need a little bit higher idle speed to be happy. Try bumping it up by opening the brass air screws.
How does that work exactly? Not trolling here at all, but genuinely curious. Any amount of additional metered airflow you supply would increase idle speeds, yes. But once the RPMs increase, the Idle Speed Circuit is going to see that and adjust the Idle Speed Motor accordingly to drop the speeds back down to defeat said modification to the RPMs.