Not scraping off the old gasket could be the cause of your erratic idle...it will leak air. As for the coolant/oil problem....coolant, check the IACV and lines going to it, it has coolant passing thru it. Check and see if you can tell where the oil is leaking from.
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2015 Ford Mustang GT Fastback - Ingot Silver - 6M - Performance Package - Gibson Catback, JLT CAI, FR 47lb injectors, BAMA E85 tune, Eibach Sportline, BMR wheel hop kit, UPR oil separator, Steeda shifter bushing/bracket
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