Mitsubishi Repair: Idle, throttle plate, foot on the gas

Question
Good Morning Anthony

I have a 97 Mit. 3000 GT (just a GT) automatic with 70K miles one it.  I got an engine lite the other day, found the battery was very low and replaced it.  The engine lite went out after replacing the battery, but now the car will not idle! One thing though, when it is cold it's ok, but as soon as it warms up, it stalls.  If I kick the A/C on it bumps the idle RMP up a little and it will idle until it gets real warm and then it will stall again. If there wern't any red lites or stop signs I would be ok. Other than this, the car runs absolutly great...Any help? (no new timing belt or tune up yet)

Thank you
Richard

Answer
Richard,
There is a component that controls your idle called the Idle Air Control (IAC) motor.  It controls the amount of air that is allowed to enter your engine when your throttle plate is closed (i.e. your car is idling without having your foot on the gas pedal).  When your engine is cold, this motor is bypassed and the amount of air is not regulated.  That's why many notice that there idle speed is higher during the winter months when they first start your car.

But when your engine warms up, your idle must be regulated and that's where the IAC starts working.  When the IAC is malfunctioning, it will not know how much air to allow to enter.  Sometimes it will allow too much air to enter; causing a very high idle.  Or sometimes it will act in the opposite manor and not allow enough air to enter your engine.  This will cause your car to stall.  So have your IAC checked.  The IAC is also referred to as an Idle Speed Control (ISC) motor.

New spark plugs, plug wires, and other tune-up item are good to replace every 30,000 miles.  A new timing belt is critical if you've never changed it before.  It should be changed every 60,000 miles.  If it's never been changed, you'll more than likely want your water pump changed as well.
Good luck!