did you make any adjustments to the mixture before you develop these symptoms or did the fault appear spontaneously?
check the following.
spark plug leads,
cold start valve-may be it continues to spray extra fuel even when your car has warmed up-hence the the uneven idle and rich mixture.-try unplugging the connector when the the car is warm. it is located on the fuel rail near the injectors ,has a bluish connector on my car ,so yours should be similar.
mine is a 1993,1.8 litre fuel injected and with a cat and hence an o2 sensor.
my gut reaction is a sensor of some sort is malfunctionoing-do you have acess to a fault code analyser to plug into the diagnostic plug in the engine compartment
hope you get a result