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It souns like you have a intake gasket problem. When the engine is cold and missing, run water over the intake manifold and check for an RPM change. If a change is noted, replace the intake manifold gaskets and check the manifold for warpage. Let me know if you have questions, thanks.
I get a 0300 code mis fire. I was going to run BG fule injector cleaner. Should I try the manifold test first?