Why is it running so rich ??
What do the wires attached to the ECT sensor look like? What ohms does the ECT measure at various temps?
With increased resistance, as these are reverse type sensors to normal thought (hotter means less resistance, colder means higher resistance) the ECU thinks it is super cold and follows suit by richening the mixture to likely unbearable levels. If you unplug the sensor, this is what happens or as the sensor dies or gets corrosion at the connector/wiring.
Check that out per the manuals and see what you find.
www.lilevo.com/mirage/
http://www.lilevo.com/mirage/89-92%20Co ... charts.pdf
Secondly, failing 02 sensors could cause the car to run badly, but it is usually a skewed ECT that throws things this badly.
It sounds good that your car starts and hits 2000 RPM, then comes down but it should not bog to 1100, jump to 1600 and back down to 900 or lower once warm. Something is out of wack and the ECU is likely compensation, assuming no other issues with vacuum hoses, gaskets, etc. Figure out the cause of running so rich, and see what happens.
Was the idle stop switch confirm to be adjusted properly and therefore working? It should be contacted as the throttle blade is just closing, and enough to seat it, as the blade closes fully. You can unplug the switch and use a test light for this. Clip on the bat+ terminal and use the needle to contact the switch connector terminal, and when the throttle touches and then closes, it should light up the test light. The ECU needs to see this function, and it can lead to stalling as you come to a stop, and weird idle in general. The 4G15 is very picky about idle, but once everything is setup correctly, it will be rock steady.