If your car RPM rise and drop intermitently during drive, exhaust produce black smoke, engine vibrating harshly, can obviously feel the car lack of power, increased fuel consumption, it might be due to excessive carbon deposit build up in the throttle body which cause unstable engine idling. Throttle body is a controllable valve which control the amount of air enter into the engine. When the air enter into intake manifold, it combine with petrol become a flammable air mixtures, which burns in the combustion chamber. However, the excessive carbon deposit build up at the throttle body and surround intake will cause a change to air channel cross sectional area, making the controlling unit could not control the idling air intake accurately., which lead to the air mixtures become too lean or too rich, abnormal combustion, and finally lead to unstable engine idling speed. Suggest to diagnose at workshop. In order to avoid and reduce the chances of throttle body faulty, a preventive maintenance must be done such as cleaning the throttle body especially if you are located at an area with frequent sandstorm.
Suggest to diagnose at workshop, usually the keypoints of diagnose are:
1. Check if there are excessive amount of cabon deposit build up in the throttle body, clean or replace it.
2. Usually there are very less cases that the throttle body needed an replacement, most of the time a dirty throttle body will require a clean up only.
3. In most cases, throttle body should be cleaned at an interval of 20k kilometer - 40k kilometer. If your car is use in a more severe environment, can shorten the throttle body cleaning interval. However, please take note cleaning the throttle body in an excessive frequency manner will also shorten its life span. Cleaning it frequently will cause the special coating in the internal part of throttle body to be depleted slowly. Once the special coating is completely gone, it will attract greasy containimant more easily.