The air valve, idle control valve or stepper motor all have one thing in common. They are designed to maintain a smooth idle by manipulating the air supply to the air inlet manifold and are computer controlled.
THINGS TO LOOK FOR
The air valve, over a period of time, may clog up and may cause the engine to idle poorly and the stepper motor may stop stepping. If the stepper decides to cause the engine to idle at around 2,000 RPM, another component could be causing the computer to control the stepper motor to idle at an incorrect setting. Another poor idle problem is the air ducting or air hose attached to the inlet manifold may be off or loose.
IS IT EXPENSIVE TO REPAIR?
If the vehicle is running rough, a thorough check may show a vacuum line off. It will be an audible whistle sound and it should be easy to see. Sometimes these are in tricky locations and may take time to find.
TEMPORARY REPAIR AND LONG TERM REPLACEMENT
This is quite simple as 80% of the time it is just a matter of slipping the hose back on. If the problem repeats itself then it may be necessary to clamp it up or replace the vacuum line.
This article is found in the Virtual mechanic CD Rom
You can download it for the price of a latte, but you will learn not to buy a lemon
By Darren Gow-Brown, Melbourne Australia ©2009