Pelican Parts Forums - Can irun my 83 SC without the lambda box and other items under the pass seat?

Lambda temperature switches are not "thermotime" switches. A thermotime switch does not need an ECU and early versions of 911 CIS basic, that have no ECU, also use thermotime switches. On your car, its sole purpose is to prevent flooding.

What edition are you reading from, my 1991 edition does not have these errors? First, no 911 with CIS has any sensors in the cylinder head. The thermotime switch is in the left side timing chain cover. The lambda temperature switches are in the right side timing chain cover and the crankcase vent cover. The cold start duty cycle is 85% and 65%, not 60%, and the cold running mixture is supplied by the reduce control pressure of the WUR, not the FV duty cycle. The 1991 version of Probst book has no 911 specific values, just generalizations. The description you suggest "peg the FV at 60% duty cycle to allow a slightly rich mixture at cold start" is not in my book and is a poor and incorrect description of the system. A 60% duty cycle is neither rich nor lean as the normal closed loop operating range is 45-60% duty cycle. The unheated O2 sensor cannot produce a reliable signal until the engine is hot so the system stays open loop at a default setting . The main cold running enrichment is performed by the reduced cold control pressure from the WUR as in CIS basic. The later cars have an additional circuit to provide 2 or 3 seconds of acceleration enrichment (75% duty cycle). This was a response to the cold start emissions test. The early 1980 version used a 85% default setting which was too rich for the test, so they backed it down to 65%, found out this caused stumbling under acceleration, then they added the cold acceleration enrichment device to compensate. It is an error to suggest there is only one open loop duty cycle.