Bro. did you get the car? I wana share my experience
I bought a city iDSi 2005 model, 27K km driven and on Petrol with NO CNG installed with 195,55, R15 tyres.
I have installed LandiRenzo CNG kit with 55L cylinder, and LendiRenzo STAP78 Advancer and Emulator.
My car runs fine on CNG giving me 135-160 Km per filling.
As soon as I started the AC, the idle RPM started to decline and finally to 0 and the car switched off. Without AC, everything is fine and also there is no problem on Patrol