I am sorry that you have not been helped yet. I just came online and saw your question
If the engine is idling up and down rhythmically, this is a faulty IAC valve, located on side of the throttle body.
If it is erratic, then it is an air leak - vacuum hose, pcv valve hose, air intake tube or intake manifold gasket. With engine idling erratically, spray each one with some carb cleaner. The one you spray that causes the idle to smooth out is the culprit and will need to be replaced
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