What affects idle speed?
In general however, there are two problems that can cause engine idle speed to fall outside of specifications: Issues with the idle control valve (or screw on a carburetor) Vacuum leaks or obstruction of fuel/air flow into the combustion chamber.
What does the idle speed adjustment do for an engine?
The idle speed control mode is used to prevent engine stall during idle. The goal is to allow the engine to idle at as low an RPM as possible yet keep the engine from running rough and stalling when power-consuming accessories, such as air-conditioning compressors and alternators, turn on.
How to adjust engine idle speed on car?
Modern car use electronic throttle body and the only way to do the correct idle adjustment is to program the computer. Some older vehicles that us throttle body with manual cable did not need any special tools to program the rpms. However, we demonstrated on a modern car how you can adjust the idle speed.
How does the IAC system affect the idle speed?
For instance, switching the air conditioning on, increases the engine load. With the IAC system, the computer immediately increases the idle speed to compensate. A cold engine runs with less efficiency and the PCM also commands a higher idle speed. This helps to circulate engine oil and prevents stalling while the engine warms.
How does electronic fuel injection affect idle speed?
When engines had carburetors, they always provided a means of adjusting the idle speed. A simple turn of a screw corrected the problem if the engine’s idle speed was too slow or too fast. With electronic Fuel injection they eliminate the manual adjustment and the computer makes all corrections to the engine’s idle speed.
What happens to an engine when the idle circuit fails?
The idle circuit eases the transition and allows a more controlled reduction of speed. When the idle circuit fails, the engine may stall when we suddenly release the throttle. A driver often sees this as the engine dying, but failure to idle is very different from a standpoint of diagnosis.