Hi, I have a lancer 1.6 GLX on factory fitted CNG.
The problem you described is very similar to mine. On petrol, the car runs absolutely fine, but sometimes on CNG, if I turn on the AC, the idle RPM goes down below 400 and i have to step on the accelerator to make it fine again. Sometimes the car runs absolutely fine on CNG even with AC on.
Could you tell me how you fixed the problem and the pictures of the ICAV?