If the idle speed is too low, the oil pump will not produce enouigh pressure. Thus, the light comes on. If the pressure is low enough, you will hear a knocking from the bearings which is not a good thing.
Now, the idle should be around 900 RPM's in park. If it is much lower, then there is a cause. Has the check engine light come on? Has your mechanic checked any of the following things:
vacuum leaks
idle air control valve
throttle position sensor
Let me know.
Joe
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Tuesday, March 2nd, 2010 AT 10:40 AM