It does sound like a vacuum leak. Have you checked all of the vacuum hoses and the base gasket on the throttle body? Also, I never heard of using WD40 to check for a leak. Most people use starting fluid. However, it can catch fire if you hit the wrong place. If you try that, keep a fire extinguisher near by.
Let me know what you find.
Joe
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Tuesday, February 2nd, 2010 AT 9:36 PM