I have a 99 LT and recently the idle is not working properly. At cold starts the engine tends to die. As the engine warms the idle is normal RPM, around 900. When the engine is at operating temp, the idle is at about 1250 RPM. I have a new air filter and my mechanic, from a phone call description from me, says it is the "stepper motor" also called the idle control mod i think. Any one?