[targa80]

Keystone5:

WHY ARE YOU SHOUTING?

This can also be a problem with the mixture control. Once warm the idle can surge high and then drop low to the point of stalling. Warm the engine and disconnect the O2 sensor plug and see if idle settles out. If it does either your O2 sensor is bad or you need to readjust the fuel /air mixture.
Recently I posted info on the sequence of the cold start to warm engine theory.

Here is the theory of the Kjetronics with lambda operation from cold start to warm operation. It might help you in figuring out your problem.

The Lambda (O2) sensor requires high temperature to operate properly. With the O2 sensor connected and the engine is cold the Kjetronics with Lambda system operates in the open-loop mode. The lambda control unit does not have a valid signal from the O2 sensor at cold start To correct drivability problems at cold start a lambda thermoswitch is installed to give the lambda control unit an additional input and insure proper fuel metering during warm-up. When the engine is cold, the thermoswitch is closed. the lambda control unit sends a fixed, slightly-rich duty cycle signal of 60% to the lamba control valve (frequency valve). when the thermoswitch warms enough to open, the control unit sends a fixed middle signal, 50% duty cycle to the frequency valve. When the lamba (O2) sensor reaches operating temperature so its signals are valid, the control unit switches to closed-loop operation. In closed-loop oeration the duty cycle signals are constantly changing cycling back and forth from 45% and 55%. so the air-fuel ratio is maintained near stoichiometric; lambda=1.

So disconnecting the O2 sensor at a cold start would do nothing to effect the running of the engine. A bad thermoswitch would effect the running of a cold engine since it would not provide the necessary signal for the control unit to run at a 60% duty cycle. Instead the control unit would put out a 50% duty cycle.

When the engine is warm and the O2 sensor is disconnected (open-loop) the contol unit would put out a constant 50% duty cycle.

The thermoswitch is something you can check for proper operation with a meter.