The normal idle speed of a car with an automatic transmission (AT) varies depending on the make and model. However, a typical range is:
* Petrol engines: 650 – 900 rpm
* Diesel engines: 650 – 850 rpm
Factors affecting automatic transmission idle speed:
*Motor size
*Fuel type
* Engine load (eg air conditioning, headlights)
* Engine and automatic transmission condition
* Computer control
Consequences of abnormal automatic transmission idle speed:
High idle speed:
* Increased fuel consumption
* Reduced engine and automatic transmission life
* Deterioration in vehicle handling
Low idle speed:
* The engine may stall
* Poor gear shifting
* Damage to the automatic transmission due to insufficient oil supply
If you notice that your vehicle’s idle speed is abnormal, it is recommended that you have it checked and repaired by a qualified mechanic.