Earlier I had the problem of engine hestitating, thanks to you, it got solved, mechanic changed the thermostat (i think without any reason) and the problem was still there so as you suggested I putted fuel injector cleaner in the gas and it worked, now the car is running ok. The new problem i had was at stop light i rpm needle starts fluctuating (around 300 rpm), with time that problem is getting away but now the engine is making noise (hmmmmm) at stop, and it happens only when the car is in gear and goes away if i put it in neutral. Also it occurs more when car is slightly hot, but I am not sure about this observation.

Kingly suggest something. Thanks