PLS HELP!
2C turbo engine (tamaraw fx)

idle w/ no aircon 850rpm and with aircon is 850rpm also. problem is during idle w/ no fan and aircon, rpm needle goes up and down and i can feel that engine is producing harsh noise and a bit of vibration w/c you can feel and hear if youre inside the car. if i turned on the fan and aircon, rpm needle stabilizes at 850 rpm and stop going up and down. engine is also very stable. fyi>>fuel injection vacuum stabilizer is working. what suppose to be the problem ? what kind of mechanic shld i go? what supposed to be checked up? tnx to everybody in advance.