A.o.A pakwheelers my honda city idsi is behaving strange. On cng the car acts normal but on petrol its idle rpms sometimes fluctuates between 750 and 950 but then sometime it acts as normal. If i stopped on signal it starts doing it and mostly comes to stable position after few repeated up and down cycles while sometime it acts normal and doesnot fluctuates at signals. My mechanic tapped the air intake passage for tuning it in cng, i suspect that the decreased air is the culprit. Plz guide me what to do.