Well as I said from the start it could be the sports cat, thats why I asked if it had been recently done and if the problem was evident afterwards.

I would check the vaccum hoses as I said as it does sound more like an air leak and it's something thats easy and free to do!

In any case the above still applies, the cone filter will only cause you problems, you are never going to gain any power, in fact maybe loose some due to the issue I mentioned already.

Best thing you can do is replace the filter with a new one, or the likes of a K&N panel filter.

Martin