Idling too fast means too much air is entering the engine. There's only two ways that can happen. One is through a vacuum leak in a vacuum hose or an engine gasket around the intake manifold on top of the engine. Sometimes you can hear a vacuum leak but first you have to know what "normal" sounds like before you can recognize "not normal". When it's idling too fast you can try pinching various vacuum hoses to see if one brings the idle speed down. If one does, follow it and pinch it in other places to locate the leak. While the engine is running and still fairly cold you can spray water on the gaskets. If you see a place where it gets sucked in and the engine slows down, you found a place to look closer for a leaking gasket. The second way for extra air to enter is through the idle air control valve on the throttle body. It is controlled by the Engine Computer and lets just enough air in to hold the idle speed at the desired level. In rare occasions it can stick after starting the engine so the idle speed won't come down to normal after providing the nice "idle flare-up" to 1500 rpm for a few seconds at engine start-up. You would find this by connecting a scanner to view live sensor data while the engine is running. If the Engine Computer is trying to reduce engine speed it is not having success. The idle air control motor and its wiring would be the place to look. If the computer is really trying to increase engine speed it is doing it in response to something it is seeing from some other sensor.
Please consider a to help us answer more questions.
Tuesday, March 15th, 2011 AT 7:03 PM