I realize that my 'oren' got some unpleasant issue. Engine vibrates due to low RPM about 600/700 RPM when air-cond kicks in. So far I am still investigate this issue closely.

It may be due to the :

1. Vacuum host that connects to the carb or
2. Belting issue or
3. Air cond compressor pulley or
4. Spark plug or
5. Distributor or etc etc...