Civic EXI manual 2006 - heating problem

Hey,

I am a brand manager at a leading company. A round 4 months back I bought a honda civic, EXi, model: 2006 (2005 shape). The car was in v good condition, ran on petrol only. done 47000 KM when i bought it. I got installed cng and todays meter reading is 55000 KM. A few days back, on motorway, the car was overheated. We brought it to lahore by a crane. didnt drive it considering heat will cause damage to the engine. Got gasket replaced two times, head faced, got new radiator, timing belt changed, timing belt bearing changed, plugs changed, air filter, oil filter, oil, did tappet adjustment, throttle service,tuning, diagnostic test on computer. But ever since the car was repaired, there is a problem with it. IT is reducing oil a bit, plus there is a problem with rpm. at idle state, or when you apply brakes the rpm falls below, car vibrates and sometimes engine turns off as well. ON CNG this is more of a problem, however on petrol the problem occurs but of less magnitude. Means the car doesnt turn off on petrol when rpm falls, but rpm does fall on petrol. Ive got cng tuning done from alot of ppl but thats not the problem. Honda people also resetted the RPM senspr, the car got perfectly fine after they resetted the sensor.but just for one day. The very next day car again got heated ( a bit) and the problem of dropping rpm prevailed right after that.

I did drive the car again n again for longer period of time..but it did not overheat. i think the heating was just once. but the rpm problem persists. What should i do for rpm? and what could the reason for oil decreasing? the car has only done 55000 km, i dont belive that rings and pistons have got weak. my driver says that there is a problem with rings and piston, however he is just guessing.

One thing more, whenever the car engines gets turned off due to low rpm, the next time i start it, it takes long self. Otherwise in normal mode, the self is v quick. no problem with the self. just when the engine turns off itself, due to rpm droppage, the next time it takes a longer self.

HELPP...!! i just have one car at home..and i am seriously depressed...