The popping noise may be a worn camshaft. At speed it may open enough to open the valve, but at idle it may not and causes the exaust or inlet valve to not open giving you the popping noise. Either that or you dropped something in the engine like a small nut or screw and it is holding the valve open. It may have bent a valve or worse.
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Tuesday, October 6th, 2009 AT 1:44 PM