I have trouble to keep the idle speed stable on my 323 protege 1990 SOHC 1800CC, I don't know if it's normal or not. Today I check the RPM with and without accessories as follow:

Idle speed with all accessories OFF = 1000RPM
Idle speed with headlight ON = 930 RPM
Idle speed with headlight and high fan ON = 880RPM
Idle speed with headlight, high fan and air conditioner ON = 650RPM

At 650RPM with all ON the engine is very rough, but If I increase to 750RPM when turn OFF all accessories the engine will rev. up to 1200RPM.

I think the ECU should keep the RPM stable as other car I have. Is the ECU gone bad? or maybe the

speed sensor is bad? or maybe other sensor?

Please help.