Since you increased the airflow to your engine, you might need to reset the spark timing also to alow for proper combustion. Advancing the timing a bit usually raises idle speed a bit. Also, the sucking air sound could be due to the increased air flow, especially with the cone filter. The stock airbox is designed to eliminate eccess noise from the intake. I put a K&N Extreme flow lid on the air cleaner for my Mustang (Basicly makes a cone filter for carbed engines) and I heard a loud sucking all the way home and thought I had a vacuum leake. It was more like a sigh of relief from my engine.